Extracted CMX3600 adapter and related sample data and tests

[apetrynet]

Link the Issue(s) this Pull Request is related to.
This PR is related to issue #1386

Summarize your change.
This PR removes the cmx_3600 adapter and related sample files and tests.
There might still be some bits and pieces left, like in the documentation.

[jminor]

This looks pretty good to me. If you want to be really clean about this change we could separate the imp -> importlib change out and land that into main before the adapter switchero. Same for the tests that use otio_json instead of cmx_3600. That would make this PR just the removal of the EDL adapter.

[apetrynet]

Yeah, I noticed the imortlib one made it's way in there after a rebase.
I'll try and revert that.

[apetrynet]

What do we do about references to the cmx adapter in the documentation? Should we do that in this PR or do a proper doc overhaul when we're done with all the adapters?

[jminor]

Lets do the documentation change after we have the adapters split out, but before landing the extract_adapters branch into main.

[apetrynet]

Looks like we need to update some of the docs after all to pass the tests.
I missed some EDL related tests and functions. Working though them now

[codecov-commenter]

Codecov Report

Merging #1487 (9bc9d52) into extract_adapters (33e0d1a) will decrease coverage by 0.73%.
The diff coverage is 85.25%.

Additional details and impacted files

@@                 Coverage Diff                  @@
##           extract_adapters    #1487      +/-   ##
====================================================
- Coverage             80.09%   79.35%   -0.74%     
====================================================
  Files                   198      193       -5     
  Lines                 21703    20617    -1086     
  Branches               4298     4152     -146     
====================================================
- Hits                  17382    16361    -1021     
+ Misses                 2174     2145      -29     
+ Partials               2147     2111      -36     

Flag	Coverage Δ
py-unittests	79.35% <85.25%> (-0.74%)	⬇️

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Impacted Files	Coverage Δ
src/opentimelineio/track.h	100.00% <ø> (ø)
...timelineio/opentimelineio/algorithms/stack_algo.py	64.28% <0.00%> (ø)
...-opentimelineio/opentimelineio/core/composition.py	100.00% <ø> (ø)
...y-opentimelineio/opentimelineio/schema/__init__.py	100.00% <ø> (ø)
...o/opentimelineio/schema/serializable_collection.py	100.00% <ø> (ø)
...y-opentimelineio/opentimelineio/schema/timeline.py	100.00% <ø> (ø)
tests/test_item.py	98.66% <ø> (ø)
tests/test_plugin_detection.py	91.46% <ø> (ø)
src/opentimelineio/stack.cpp	57.35% <33.33%> (ø)
...entimelineio-bindings/otio_serializableObjects.cpp	36.09% <44.82%> (ø)
... and 37 more

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