Remove install_jax and rename have_jax

[kratman]

Description

Removes the deprecated install_jax() method

Fixes #4131

Key checklist:

• No style issues: $ pre-commit run (or $ nox -s pre-commit) (see CONTRIBUTING.md for how to set this up to run automatically when committing locally, in just two lines of code)
• All tests pass: $ python run-tests.py --all (or $ nox -s tests)
• The documentation builds: $ python run-tests.py --doctest (or $ nox -s doctests)

You can run integration tests, unit tests, and doctests together at once, using $ python run-tests.py --quick (or $ nox -s quick).

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.42%. Comparing base (8057c16) to head (b26c99f).
Report is 202 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4362      +/-   ##
===========================================
- Coverage    99.46%   99.42%   -0.04%     
===========================================
  Files          289      289              
  Lines        22200    22153      -47     
===========================================
- Hits         22081    22026      -55     
- Misses         119      127       +8     

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[Saransh-cpp]

Thanks, @kratman!

[kratman]

@Saransh-cpp, @agriyakhetarpal I pull out the has_jax() part for now

[kratman]

Coverage failure is unrelated

Part of the code under discussion was removed