Rm build_rtd_docs CI job and its dependencies

[senecameeks]

Fixes #6416

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a3eed6b) 97.81% compared to head (00dfb84) 97.81%.
Report is 2 commits behind head on main.

❗ Current head 00dfb84 differs from pull request most recent head ebe1283. Consider uploading reports for the commit ebe1283 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6417   +/-   ##
=======================================
  Coverage   97.81%   97.81%           
=======================================
  Files        1111     1111           
  Lines       97115    97115           
=======================================
  Hits        94994    94994           
  Misses       2121     2121           

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[pavoljuhas]

Looks good, but there are few more leftovers -

$ git grep -n -i "readthedocs.{0,30}cirq|rtd" | grep -v -i image/png
.dockerignore:24:rtd_docs/generated
.gitignore:25:rtd_docs/generated
.readthedocs.yml:7:      - requirements: rtd_docs/requirements.txt
.readthedocs.yml:9:  configuration: rtd_docs/conf.py
README.rst:19:.. image:: https://readthedocs.org/projects/cirq/badge/?version=latest
README.rst:20:  :target: https://readthedocs.org/projects/cirq/versions/
dev_tools/incremental_coverage.py:24:    r'^rtd_docs/.+',  # Environment-heavy code.

We should remove the .readthedocs.yml configuration file as there is nothing to build at RTD now. :-)

[pavoljuhas]

The hanging Build docs CI job may need to be somehow deactivated in our GitHub page.

@dstrain115 , @95-martin-orion - can you PTAL?

[senecameeks]

Re: @pavoljuhas comment-- someone should be able to disable the workflow by navigating to the Actions tab on github and disabling the workflow. I don't think I have sufficient permissions to do it myself since I'm not seeing an option to do it.

@dstrain115 , @95-martin-orion can either of you disable the deprecated Build Docs CI job on the GUI?

[pavoljuhas]

LGTM, Thank you!