Remove rebase-comment action

[Bisaloo]

This can now be done with official tooling: https://github.blog/changelog/2022-02-03-more-ways-to-keep-your-pull-request-branch-up-to-date/.

I'd like to remove this action to remove the API_TOKEN_GITHUB entirely.

[codecov]

Codecov Report

Merging #199 (233f930) into master (4f583a5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #199   +/-   ##
=======================================
  Coverage   54.56%   54.56%           
=======================================
  Files          19       19           
  Lines        1468     1468           
=======================================
  Hits          801      801           
  Misses        667      667           

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[nikosbosse]

<3 Amazing!