opencv: drop workarounds, update test to use shared lib

[cho-m]

Not sure what original reason for PYTHONPATH workaround but brew should sanitize environment variables. Within brew, only Language::Python.each_python manipulates PYTHONPATH but that isn't used within official taps.

Protobuf workarounds haven't been needed since 4.9.0 opencv/opencv@6e4280e

Test has been a simple version check which we usually don't like. Added a minor update to at least try using part of API that need shared libraries (some of https://docs.opencv.org/4.11.0/db/deb/tutorial_display_image.html). May be worth expanding to a larger example that uses more features.

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Also trying to see if failure in #208051 is specific to those changes.

[cho-m]

Same failure as other PR with unrelated set of changes. May be something else changed and has broken binaries:

  ==> python3.13 -c 'import cv2; print(cv2.__version__)'
  WARNING: All log messages before absl::InitializeLog() is called are written to STDERR
  E0000 00:00:1740341130.525890   53511 descriptor_database.cc:550] Invalid file descriptor data passed to EncodedDescriptorDatabase::Add().
  F0000 00:00:1740341130.525922   53511 descriptor.cc:2248] Check failed: GeneratedDatabase()->Add(encoded_file_descriptor, size) 
  *** Check failure stack trace: ***
  Aborted (core dumped)

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We did successfully build OpenCV recently (Feb 7th).

No changes in python@3.13, protobuf or abseil which is part of above error message.