[ISSUE-1229] Resolve failing linter: unused and enable back

[jameskim0987]

Fixes issue https://github.com/digitalocean/terraform-provider-digitalocean/issues/1229

Output of make lint after enabling back unused:

jameskim:~/workspace/terraform-provider-digitalocean $ make lint
INFO golangci-lint has version 1.61.0 built with go1.23.1 from a1d6c56 on 2024-09-09T14:33:19Z
INFO [config_reader] Config search paths: [./ /Users/jameskim/workspace/terraform-provider-digitalocean /Users/jameskim/workspace /Users/jameskim /Users /]
INFO [config_reader] Used config file .golangci.yml
WARN [config_reader] The configuration option `linters.errcheck.ignore` is deprecated, please use `linters.errcheck.exclude-functions`.
INFO [lintersdb] Active 7 linters: [gofmt goimports gosimple govet staticcheck unconvert unused]
INFO [loader] Go packages loading at mode 575 (name|types_sizes|compiled_files|exports_file|imports|deps|files) took 3.105408387s
INFO [runner/filename_unadjuster] Pre-built 0 adjustments in 60.098237ms
INFO [linters_context/goanalysis] analyzers took 0s with no stages
INFO [runner] Issues before processing: 114, after processing: 1
INFO [runner] Processors filtering stat (in/out): uniq_by_line: 1/1, diff: 1/1, invalid_issue: 114/114, identifier_marker: 114/114, exclude-rules: 114/1, max_per_file_from_linter: 1/1, source_code: 1/1, path_shortener: 1/1, severity-rules: 1/1, fixer: 1/1, filename_unadjuster: 114/114, skip_files: 114/114, exclude:
 114/114, max_same_issues: 1/1, sort_results: 1/1, cgo: 114/114, path_prettifier: 114/114, nolint: 1/1, max_from_linter: 1/1, path_prefixer: 1/1, skip_dirs: 114/114, autogenerated_exclude: 114/114
INFO [runner] processing took 31.851946ms with stages: identifier_marker: 16.062064ms, invalid_issue: 5.125848ms, nolint: 3.88447ms, autogenerated_exclude: 2.265732ms, path_prettifier: 1.981865ms, exclude-rules: 1.091937ms, source_code: 915.043µs, skip_dirs: 478.295µs, cgo: 25.83µs, filename_unadjuster: 5.481µs, ma
x_from_linter: 4.065µs, uniq_by_line: 2.674µs, path_shortener: 2.445µs, max_per_file_from_linter: 2.036µs, max_same_issues: 1.395µs, exclude: 528ns, fixer: 517ns, skip_files: 493ns, sort_results: 458ns, diff: 311ns, severity-rules: 266ns, path_prefixer: 193ns
INFO [runner] linters took 428.258507ms with stages: goanalysis_metalinter: 395.938952ms
digitalocean/kubernetes/resource_kubernetes_cluster_test.go:884:6: func `testAccDigitalOceanKubernetesConfigBasic5` is unused (unused)
func testAccDigitalOceanKubernetesConfigBasic5(testClusterVersion string, rName string) string {
     ^
INFO File cache stats: 1 entries of total size 44.3KiB
INFO Memory: 38 samples, avg is 29.6MB, max is 54.2MB
INFO Execution took 3.617533898s
make: *** [lint] Error 1

Looking through the test, I found that essentially testAccDigitalOceanKubernetesConfigBasic4 covers what testAccDigitalOceanKubernetesConfigBasic5 was trying to achieve. The only difference I observed was testAccDigitalOceanKubernetesConfigBasic4 has addition checks for surge_upgrade and ha checks.

Changes made in this PR:

1. add back unused linter in .golangci.yml
2. remove the unused function testAccDigitalOceanKubernetesConfigBasic5 ( redundant test function )

Output of make lint after enabling back unused with the PR changes:

jameskim:~/workspace/terraform-provider-digitalocean $ make lint
INFO golangci-lint has version 1.61.0 built with go1.23.1 from a1d6c56 on 2024-09-09T14:33:19Z
INFO [config_reader] Config search paths: [./ /Users/jameskim/workspace/terraform-provider-digitalocean /Users/jameskim/workspace /Users/jameskim /Users /]
INFO [config_reader] Used config file .golangci.yml
WARN [config_reader] The configuration option `linters.errcheck.ignore` is deprecated, please use `linters.errcheck.exclude-functions`.
INFO [lintersdb] Active 7 linters: [gofmt goimports gosimple govet staticcheck unconvert unused]
INFO [loader] Go packages loading at mode 575 (exports_file|files|name|types_sizes|compiled_files|deps|imports) took 4.866297169s
INFO [runner/filename_unadjuster] Pre-built 0 adjustments in 127.308393ms
INFO [linters_context/goanalysis] analyzers took 810.269674ms with top 10 stages: buildir: 188.196073ms, unconvert: 118.508405ms, goimports: 96.291208ms, S1038: 62.830719ms, gofmt: 58.418609ms, S1002: 26.114926ms, SA4016: 25.214608ms, unused: 19.453293ms, SA5009: 17.791958ms, SA4019: 15.474008ms
INFO [runner] Issues before processing: 113, after processing: 0
INFO [runner] Processors filtering stat (in/out): filename_unadjuster: 113/113, skip_files: 113/113, autogenerated_exclude: 113/113, identifier_marker: 113/113, path_prettifier: 113/113, exclude-rules: 113/0, cgo: 113/113, invalid_issue: 113/113, skip_dirs: 113/113, exclude: 113/113
INFO [runner] processing took 20.3465ms with stages: identifier_marker: 8.589125ms, autogenerated_exclude: 7.793611ms, path_prettifier: 2.124903ms, exclude-rules: 1.253684ms, skip_dirs: 478.955µs, cgo: 79.262µs, invalid_issue: 12.871µs, filename_unadjuster: 6.048µs, nolint: 2.099µs, max_same_issues: 1.322µs, skip_files: 658ns, uniq_by_line: 596ns, fixer: 487ns, exclude: 421ns, max_from_linter: 407ns, sort_results: 395ns, diff: 375ns, max_per_file_from_linter: 318ns, path_shortener: 286ns, source_code: 284ns, severity-rules: 221ns, path_prefixer: 172ns
INFO [runner] linters took 3.148740789s with stages: goanalysis_metalinter: 3.127650354s
INFO File cache stats: 0 entries of total size 0B
INFO Memory: 83 samples, avg is 45.2MB, max is 132.2MB
INFO Execution took 8.178608358s

[jameskim0987]

Hi @loosla, this PR is ready for review

[loosla]

:rocket: Excellent work! Thank you for your contribution.

[jameskim0987]

@loosla Thank you!