Remove Plugin schema execution_scope parameter

[ssteinbach]

When the plugin system was originally designed for the adapter system, the idea was that adapters could be implemented in other languages by sub shelling out. It was simpler to implement that directly via the extern_* pattern seen in the RV and Maya adapters, and now the library is emphasizing native support. This feature was never implemented, so this PR removes the parameter from the library.

This PR follows #1395

Closes #728

[codecov-commenter]

Codecov Report

Merging #1428 (7a218f0) into main (41ceb58) will decrease coverage by 0.00%.
The diff coverage is 83.33%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1428      +/-   ##
==========================================
- Coverage   86.38%   86.38%   -0.01%     
==========================================
  Files         201      201              
  Lines       20860    20854       -6     
  Branches     2298     2298              
==========================================
- Hits        18020    18014       -6     
  Misses       2244     2244              
  Partials      596      596              

Flag	Coverage Δ
py-unittests	86.38% <83.33%> (-0.01%)	⬇️

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

Impacted Files	Coverage Δ
...-opentimelineio/opentimelineio/adapters/adapter.py	89.00% <ø> (ø)
...timelineio/opentimelineio/plugins/python_plugin.py	88.88% <ø> (-0.35%)	⬇️
tests/test_adapter_plugin.py	87.75% <ø> (-0.09%)	⬇️
tests/test_hooks_plugins.py	97.72% <ø> (-0.06%)	⬇️
tests/test_media_linker.py	95.65% <ø> (-0.10%)	⬇️
...-opentimelineio/opentimelineio/schema/schemadef.py	94.73% <50.00%> (ø)
src/py-opentimelineio/opentimelineio/hooks.py	100.00% <100.00%> (ø)
...c/py-opentimelineio/opentimelineio/media_linker.py	83.33% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 41ceb58...7a218f0. Read the comment docs.

[meshula]

This looks good to me. Are there knock-on affects to adapters outside of this repository? i.e. is it possible there are external callers to MediaLinker that might need to modify source with one less parameter?

[ssteinbach]

I've tested against our proprietary plugin set and it looks good, trying to find an additional tester.

[ssteinbach]

Tested externally now, looks good there too (thanks @apetrynet and @reinecke).