Remove deprecated each_child and each_clip functions

[markreidvfx]

This PR removes deprecated Python functions.

Changes ported over from
AcademySoftwareFoundation/OpenTimelineIO#1437

[codecov-commenter]

Codecov Report

Base: 90.15% // Head: 90.15% // No change to project coverage 👍

Coverage data is based on head (fc1e6ce) compared to base (c432f29).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #13   +/-   ##
=======================================
  Coverage   90.15%   90.15%           
=======================================
  Files           3        3           
  Lines        1107     1107           
=======================================
  Hits          998      998           
  Misses        109      109           

Flag	Coverage Δ
unittests	90.15% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...tio_aaf_adapter/adapters/aaf_adapter/aaf_writer.py	97.30% <100.00%> (ø)
..._aaf_adapter/adapters/advanced_authoring_format.py	85.93% <100.00%> (ø)

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[JeanChristopheMorinPerso]

LGTM

[meshula]

lgtm