[3.12] pythongh-127553: Remove outdated TODO comment in _pydatetime (pythonGH-127564) (python#128501)

(cherry picked from commit e8b6b39)

Co-authored-by: Beomsoo Kim <[email protected]>

Author: miss-islington

Lib/_pydatetime.py

@@ -2313,7 +2313,6 @@ def __reduce__(self):
 
 def _isoweek1monday(year):
     # Helper to calculate the day number of the Monday starting week 1
-    # XXX This could be done more efficiently
     THURSDAY = 3
     firstday = _ymd2ord(year, 1, 1)
     firstweekday = (firstday + 6) % 7  # See weekday() above