build: Remove sphinx-togglebutton from 'docs' extra

[matthewfeickert]

Description

Remove sphinx-togglebutton dependency from the 'docs' extra as sphinx-togglebutton was used only to make a instructional admonition into a toggleable dropdown. The admonition was removed in PR #2187 and so sphinx-togglebutton is no longer needed.

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 sphinx-togglebutton dependency from the 'docs' extra as
  sphinx-togglebutton was used only to make a instructional admonition
  into a toggleable dropdown. The admonition was removed in PR #2187 and so
  sphinx-togglebutton is no longer needed.
* Remove use of sphinx_togglebutton extension from docs/conf.py.
* Amends PR https://github.com/scikit-hep/pyhf/pull/2187.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (b8e942a) 98.30% compared to head (986bf6a) 98.30%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2190   +/-   ##
=======================================
  Coverage   98.30%   98.30%           
=======================================
  Files          69       69           
  Lines        4533     4533           
  Branches      801      801           
=======================================
  Hits         4456     4456           
  Misses         45       45           
  Partials       32       32           

Flag	Coverage Δ
contrib	97.88% <ø> (ø)
doctest	61.12% <ø> (ø)
unittests-3.10	96.31% <ø> (ø)
unittests-3.11	96.31% <ø> (ø)
unittests-3.8	96.33% <ø> (ø)
unittests-3.9	96.36% <ø> (ø)

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[matthewfeickert]

I'm going to approve and merge this myself. As always, PRs approved by a single core dev can be reverted as needed by the rest of the dev team.