fix typo, clean up test_traceback_frame_removal

[jakkdl]

fixes a typo that was added in #3269, and cleans up test_traceback_frame_removal which I noticed when reading the code base the other day.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00000%. Comparing base (ca218b2) to head (c8c04b6).
⚠️ Report is 43 commits behind head on main.

Additional details and impacted files

@@               Coverage Diff               @@
##                 main        #3272   +/-   ##
===============================================
  Coverage   100.00000%   100.00000%           
===============================================
  Files             127          127           
  Lines           19259        19257    -2     
  Branches         1301         1301           
===============================================
- Hits            19259        19257    -2     

Files with missing lines	Coverage Δ
src/trio/_core/_tests/test_run.py	100.00000% <100.00000%> (ø)

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[webknjaz]

I'm good with the typo fix, haven't checked other changes.

[jakkdl]

The test cleanup is very simple, we now run with strict_exception_groups so we no longer need to force two exceptions in order to get an ExceptionGroup.