ci: Remove setuptools uprgrade as no longer backend

[matthewfeickert]

Description

Remove setuptools installs and upgrades from CI workflows and the Dockerfile build as it should not be required by any component of pyhf.

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Remove setuptools installs and upgrades from CI workflows and the
  Dockerfile build as it should not be required by any component of pyhf.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.21%. Comparing base (a0caf31) to head (70dd42b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2519   +/-   ##
=======================================
  Coverage   98.21%   98.21%           
=======================================
  Files          69       69           
  Lines        4543     4543           
  Branches      804      804           
=======================================
  Hits         4462     4462           
  Misses         48       48           
  Partials       33       33           

Flag	Coverage Δ
contrib	97.79% <ø> (ø)
doctest	98.08% <ø> (ø)
unittests-3.10	96.23% <ø> (ø)
unittests-3.11	96.23% <ø> (ø)
unittests-3.12	96.23% <ø> (ø)
unittests-3.8	96.25% <ø> (ø)
unittests-3.9	96.27% <ø> (ø)

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