They don't seem to fit in any existing subsection and creating a section
just for them seems silly, so move them, together with other
single-entry subsections, to "misc.".

To compensate the loss of the "margins and autoscaling subsection", add
mention of autoscaling in the first line of the sticky_edges docstring,
to keep that term ctrl-f'able on the API docs page.

noticed while reviewing#13432.

PR Summary

PR Checklist

• Has Pytest style unit tests
• Code isFlake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way