Remove embedding_in_tk_canvas, which demonstrated a private API.

[anntzer]

PR Summary

See discussion in #11507.

PR Checklist

• Has Pytest style unit tests
• Code is PEP 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

[dstansby]

👍 anyone feel free to merge if/when all the builds pass

[WeatherGod]

We should fix the example. It is meant to show how to embed a canvas into a tk app, The blitting part is actually not really needed, we can do something else instead.

[anntzer]

Is https://matplotlib.org/gallery/user_interfaces/embedding_in_tk_sgskip.html#sphx-glr-gallery-user-interfaces-embedding-in-tk-sgskip-py not good enough for you? This (currently being removed) example is a lower-level API but it's not clear getting a public API for that is really helpful (it still requires instantiating a FigureCanvasAgg (duh) so you may as well instantiate a FigureCanvasTkAgg instead and fetch the underlying tk widget with get_tk_canvas() (which is exactly what the other example does)).

[WeatherGod]

Ah, you are right. I read the example too quickly. Carry on.