Remove the last remains of opentimelineio_contrib

[apetrynet]

CI is failing in a separate PR #1944 which uncovered some remaining "opentimelineio_contrib" statements. This PR hopefully removes the remaining statements

• Removed the remaining opentimelineio_contrib statements
• Updated "write an adapter" to point to the adapter repos under the OpenTimelineIO org.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.00%. Comparing base (c0e97b0) to head (12fe74d).
⚠️ Report is 72 commits behind head on main.

❌ Your changes status has failed because you have indirect coverage changes. Learn more about Unexpected Coverage Changes and reasons for indirect coverage changes.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1946      +/-   ##
==========================================
+ Coverage   84.11%   85.00%   +0.88%     
==========================================
  Files         198      181      -17     
  Lines       22241    13074    -9167     
  Branches     4687     1206    -3481     
==========================================
- Hits        18709    11113    -7596     
+ Misses       2610     1778     -832     
+ Partials      922      183     -739     

Flag	Coverage Δ
py-unittests	85.00% <ø> (+0.88%)	⬆️

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see 139 files with indirect coverage changes

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[meshula]

lgtm, thanks for repairing that