chore!: remove deprecated "platform-improvements" feedback survey name

[zimeg]

Changelog

We removed the deprecated platform-improvements survey name from the feedback command to now prefer the slack-platform name when providing Slack Platform feedback.

Summary

🪓 This PR removes the deprecated SlackPlatformFeedbackDeprecated constant and the backwards-compatibility mapping that redirected --name platform-improvements to --name slack-platform. Using the old name will now return an invalid feedback name error.

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.05%. Comparing base (5100c02) to head (591ae18).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #465      +/-   ##
==========================================
- Coverage   71.06%   71.05%   -0.02%     
==========================================
  Files         220      220              
  Lines       18522    18519       -3     
==========================================
- Hits        13163    13159       -4     
  Misses       4181     4181              
- Partials     1178     1179       +1     

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[srtaalej]

code health mhm ✅ ✅ ✅

[zimeg]

@srtaalej It's nice to keep the maintained paths tested well! 🚢