Drop mock dev/test dependency, which is not actually used.

[musicinmybrain]

Description

Drop mock dependency, which is not actually used.

See also https://fedoraproject.org/wiki/Changes/DeprecatePythonMock

Checklist

• [x] I've added this contribution to the changelog.rst.
• [x] I installed pre-commit hooks (pip install pre-commit && pre-commit install), and ran black on my code.
• [x] Please squash merge this pull request (uncheck if you'd like us to merge as multiple commits)

[codecov-commenter]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@e5486a5). Click here to learn what that means. The diff coverage is 65.86%.

@@            Coverage Diff            @@
##             master     #115   +/-   ##
=========================================
  Coverage          ?   29.24%           
=========================================
  Files             ?        6           
  Lines             ?     2500           
  Branches          ?        0           
=========================================
  Hits              ?      731           
  Misses            ?     1769           
  Partials          ?        0           

Impacted Files	Coverage Δ
pgspecial/help/commands.py	0.20% <ø> (ø)
pgspecial/main.py	38.18% <52.17%> (ø)
pgspecial/dbcommands.py	33.60% <66.73%> (ø)
pgspecial/iocommands.py	42.69% <68.05%> (ø)
pgspecial/namedqueries.py	92.00% <75.00%> (ø)
pgspecial/__init__.py	100.00% <100.00%> (ø)

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