Remove dead jsonargparse<4.39 skip guards

[bhimrazy]

What does this PR do?

Removes @pytest.mark.skipif(compare_version("jsonargparse", operator.lt, "4.39"), ...) guards in test_cli.py — the jsonargparse floor is pinned to >=4.39.0 in requirements/pytorch/extra.txt, so these were always false. Also drops the now-unused operator and compare_version imports.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79%. Comparing base (fbdf042) to head (22ea341).
✅ All tests successful. No failed tests found.
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HEAD has 2318 uploads less than BASE

Flag	BASE (fbdf042)	HEAD (22ea341)
cpu	583	60
python	29	3
lightning_fabric	222	0
pytest	297	0
python3.12	205	21
python3.10	30	3
lightning	149	15
python3.13	170	18
python3.12.7	89	9
python3.11	60	6
pytorch2.2.2	15	3
pytest-full	286	60
pytorch2.3	15	3
pytorch2.1	29	6
pytorch_lightning	212	45
pytorch2.9	29	6
pytorch2.13	29	6
pytorch2.4.1	14	3
pytorch2.5.1	15	3
pytorch2.10	27	6
pytorch2.12	27	6
pytorch2.11	28	6
pytorch2.8	29	6
pytorch2.7	14	3
pytorch2.6	15	3

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #21848     +/-   ##
=========================================
- Coverage      87%      79%     -8%     
=========================================
  Files         270      267      -3     
  Lines       24074    24015     -59     
=========================================
- Hits        20906    18867   -2039     
- Misses       3168     5148   +1980