[heroku] remove deprecated plugin

[atoulme]

Description:
Remove plugin deprecated since v0.112.0.

Please use https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/processor/resourcedetectionprocessor#heroku instead.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 38.89%. Comparing base (a89755c) to head (157bde9).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7102      +/-   ##
==========================================
+ Coverage   38.86%   38.89%   +0.02%     
==========================================
  Files         348      347       -1     
  Lines       24246    24221      -25     
==========================================
- Hits         9423     9420       -3     
+ Misses      14041    14019      -22     
  Partials      782      782              

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