PR Summary

/tutorials/intermediate/gridspec was pretty stale, in particular users almost never need to access gridspec directly anymore with subplot_mosaic and subfigures providing higher-level interfaces to those features. I also moved the tutorial to a new name arranging_axes instead of gridspec since the tutorial is now more general.

PR Checklist

Tests and Styling

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (install flake8-docstrings and run flake8 --docstring-convention=all).

Documentation

• New features are documented, with examples if plot related.
• 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).
• Documentation is sphinx and numpydoc compliant (the docs should build without error).