Remove unused deprecated "test_suite" directive from setup.py

[penguinolog]

Checklist

• I've ensured that similar functionality has not already been implemented
• I've ensured that similar functionality has not earlier been proposed and declined
• I've branched off the master or python-dual-support branch
• I've merged fresh upstream into my branch recently
• I've ran tox successfully in local environment
• I've included docstrings and/or documentation and/or examples for my code (if this is a new feature)

[coveralls]

Pull Request Test Coverage Report for Build 7397352127

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 68.945%

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Totals
Change from base Build 7397133223:	0.0%
Covered Lines:	7945
Relevant Lines:	11591

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💛 - Coveralls

[ulidtko]

How is it deprecated? As #728 shows, it's also definitely not unused.

[penguinolog]

How is it deprecated? As #728 shows, it's also definitely not unused.

https://setuptools.pypa.io/en/latest/deprecated/commands.html#test-build-package-and-run-a-unittest-suite

Officially deprecated by setuptools

[ulidtko]

Alright, makes sense, there's tox.ini instead setting the tests entrypoint ✔️