refactor: remove unused parameter from pick function

[alexandear]

This PR refactors internal function: remove the parameter f func(n ast.Node) []ast.Node from pick because it is always nil.

This refactoring was found by the unparam linter:

❯ go run mvdan.cc/unparam@latest ./...
lint/file.go:191:22: (*File).disabledIntervals$3 - filename is unused
lint/file.go:191:95: (*File).disabledIntervals$3 - result 0 ([]github.com/mgechev/revive/lint.DisabledInterval) is always nil
rule/utils.go:98:54: pick - f always receives nil
exit status 1

[chavacava]

Thank you @alexandear