There's really two separate fixes here:

• Move isDefault_{maj,min}{loc,fmt} tracking to the Ticker instances,
  where they logically belong (note the previous need to additionally
  track them manually on axes removal, when that info was tracked on
  the Axis). This has the side effect of fixing removal of sharex'd
  polar axes, as ThetaLocators rely on _AxisWrappers which don't have
  that isDefault attribute. (Note that the patch would have resulted
  in a net decrease of lines of code if it didn't need to maintain
  backcompat on isDefault_foos).ClosesRemoval of x-shared polar axes causes crash #19988. Split out ofAllow sharing Locators and Formatters across Axises. #13482.

• Ensure that RadialLocator correctly propagates Axis information to
  the linear locator it wraps (consistently with ThetaLocator), so that
  when an axes is removed the wrapped linear locator doesn't stay
  pointing at an obsolete axes. This, together with the first patch,
  fixes removal of sharey'd polar axes.ClosesRemoval of y-shared polar axes causes crash at draw time #19989.

PR Summary

PR Checklist

• Has pytest style unit tests (andpytest passes).
• IsFlake 8 compliant (runflake8 on changed files to check).
• New features are documented, with examples if plot related.
• Documentation is sphinx and numpydoc compliant (the docs shouldbuild without error).
• Conforms to Matplotlib style conventions (installflake8-docstrings and runflake8 --docstring-convention=all).
• New features have an entry indoc/users/next_whats_new/ (follow instructions in README.rst there).
• API changes documented indoc/api/next_api_changes/ (follow instructions in README.rst there).