Remove connector close workaround for older Python versions

[bdraco]

The TODO is fixed on all supported versions which was added in #6321

python/cpython#84132

Note this code is not present in 3.x

[bdraco]

I think we need to drop the test_release_proto_closed_future test as well

[codspeed-hq]

CodSpeed Performance Report

Merging #9818 will not alter performance

_{Comparing remove_todo_connector (12a2ba5) with master (26f096d)}

Summary

✅ 17 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.69%. Comparing base (7a46f64) to head (12a2ba5).
Report is 664 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9818      +/-   ##
==========================================
- Coverage   98.69%   98.69%   -0.01%     
==========================================
  Files         118      118              
  Lines       36026    36017       -9     
  Branches     4280     4279       -1     
==========================================
- Hits        35557    35548       -9     
  Misses        315      315              
  Partials      154      154              

Flag	Coverage Δ
CI-GHA	98.58% <ø> (-0.01%)	⬇️
OS-Linux	98.27% <ø> (-0.01%)	⬇️
OS-Windows	96.05% <ø> (-0.01%)	⬇️
OS-macOS	97.34% <ø> (-0.01%)	⬇️
Py-3.10.11	97.19% <ø> (-0.02%)	⬇️
Py-3.10.15	97.80% <ø> (+0.05%)	⬆️
Py-3.11.10	97.78% <ø> (-0.07%)	⬇️
Py-3.11.9	97.24% <ø> (-0.02%)	⬇️
Py-3.12.7	98.33% <ø> (-0.01%)	⬇️
Py-3.13.0	98.32% <ø> (-0.01%)	⬇️
Py-3.9.13	97.11% <ø> (-0.01%)	⬇️
Py-3.9.20	97.66% <ø> (-0.01%)	⬇️
Py-pypy7.3.16	97.28% <ø> (+<0.01%)	⬆️
VM-macos	97.34% <ø> (-0.01%)	⬇️
VM-ubuntu	98.27% <ø> (-0.01%)	⬇️
VM-windows	96.05% <ø> (-0.01%)	⬇️

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