Suggestion: depend on matplotlib-base instead of matplotlib

[regro-cf-autotick-bot]

I noticed that this recipe depends on matplotlib instead of
matplotlib-base. Unless you need pyqt, recipes should depend only on matplotlib-base.
This PR makes this change.
Notes and instructions for merging this PR:

1. Make sure that the recipe can indeed only depend on matplotlib-base.
2. Please merge the PR only after the tests have passed.
3. Feel free to push to the bot's branch to update this PR if needed.

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[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

I do have some suggestions for making it better though...

For recipe:

• Whenever possible python packages should use pip. See https://conda-forge.org/docs/maintainer/adding_pkgs.html#use-pip

[megies]

included this in #31