docs: remove duplicate readthedocs yaml

[tigarmo]

This happened during the starbase merge; starbase uses .readthedocs.yaml, but we already had a .readthedocs.yml. Let's prefer upstream's.

• Have you followed the guidelines for contributing?
• Have you signed the CLA?
• Have you successfully run tox?

---

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@6b34e46). Click here to learn what that means.
The diff coverage is n/a.

❗ Current head 8bcb35c differs from pull request most recent head de0ff99. Consider uploading reports for the commit de0ff99 to get more accurate results

@@           Coverage Diff           @@
##             main      #76   +/-   ##
=======================================
  Coverage        ?   88.09%           
=======================================
  Files           ?       13           
  Lines           ?      630           
  Branches        ?      125           
=======================================
  Hits            ?      555           
  Misses          ?       61           
  Partials        ?       14