Drop unused dependencies

[braingram]

An attempted regtest run with python 3.13 showed a failure when the test machine failed to build getch:
https://github.com/spacetelescope/RegressionTests/actions/runs/12264011982/job/34217036983?pr=183#step:14:38
I don't see any uses of this package. (FWIW The python 3.13 tests aren't failing in the CI here so the above failure could be seen as a bug in the proposed regtest test machine changes).

This PR removes unused dependencies:

• getch: looks like a dead package (no release since 2013): https://pypi.org/project/getch/
• colorama: this isn't imported
• flake8: this was replaced by ruff

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.32%. Comparing base (244858c) to head (13de9ec).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #190      +/-   ##
==========================================
+ Coverage   90.02%   90.32%   +0.29%     
==========================================
  Files          17       17              
  Lines        2165     2170       +5     
==========================================
+ Hits         1949     1960      +11     
+ Misses        216      210       -6     

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[schlafly]

Thanks!

[schlafly]

(and FWIW, e.g. getch and colorama date back to the original skeleton commits before I started and we actually had written any non-boilerplate code, so ... no problem dropping them!)