[Fix] Deprecate the support for "python setup.py test"

[ly015]

Motivation

Refer to open-mmlab/mmcv#1637

Modification

BC-breaking (Optional)

Use cases (Optional)

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit tests to ensure correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (dev-0.23@fb07c95). Click here to learn what that means.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             dev-0.23    #1135   +/-   ##
===========================================
  Coverage            ?   82.46%           
===========================================
  Files               ?      203           
  Lines               ?    16069           
  Branches            ?     2862           
===========================================
  Hits                ?    13251           
  Misses              ?     2095           
  Partials            ?      723           

Flag	Coverage Δ
unittests	82.40% <0.00%> (?)

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