Minor improvements

[0xnm]

What does this PR do?

This change does some minor improvements:

• Removes mentions of the legacy DC names.
• Removes unused class.
• Makes use of Response#body taking into account Closeable interface (to avoid warnings from OkHttp about response body being leaked).

Review checklist (to be filled by reviewers)

• [ ] Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• [ ] Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• [ ] Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)

[codecov-commenter]

Codecov Report

Merging #155 (5d77cbf) into develop (df5e4b3) will increase coverage by 0.19%. The diff coverage is 75.00%.

@@              Coverage Diff              @@
##             develop     #155      +/-   ##
=============================================
+ Coverage      86.72%   86.92%   +0.19%     
- Complexity       178      179       +1     
=============================================
  Files             21       21              
  Lines            580      581       +1     
  Branches          73       73              
=============================================
+ Hits             503      505       +2     
  Misses            48       48              
+ Partials          29       28       -1     

Impacted Files	Coverage Δ
.../datadog/gradle/plugin/DdExtensionConfiguration.kt	100.00% <ø> (ø)
...m/datadog/gradle/plugin/DdMappingFileUploadTask.kt	88.49% <ø> (ø)
...m/datadog/gradle/plugin/internal/OkHttpUploader.kt	84.55% <75.00%> (+0.13%)	:arrow_up:

... and 1 file with indirect coverage changes