Don't alphabetically sort the arrowstyles; the order of definition in
the source makes more sense. (The sorted call was necessary back when
dicts were unsorted.) Also move the definition of BracketAB after
BracketA and BracketB, for consistency with the other arrow styles.

Various small fixes (making the axis invisible is already done by
frameon=False, no need to use mathtext).

before:

after:

PR Summary

PR Checklist

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (run flake8 on changed files to check).
• New features are documented, with examples if plot related.
• Documentation is sphinx and numpydoc compliant (the docs should build without error).
• Conforms to Matplotlib style conventions (install flake8-docstrings and run flake8 --docstring-convention=all).
• New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).