Fix requiring OpenGL on macOS.

[iche033]

🦟 Bug fix

Related: osrf/homebrew-simulation#2237 (comment)

Summary

#840 explicitly made OpenGL a required component but that broke pkg-config in homebrew. This PR reverts the change for macOS.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #844 (9101bbb) into gz-rendering7 (80d41b2) will not change coverage.
The diff coverage is n/a.

❗ Current head 9101bbb differs from pull request most recent head 4bd723e. Consider uploading reports for the commit 4bd723e to get more accurate results

@@              Coverage Diff               @@
##           gz-rendering7     #844   +/-   ##
==============================================
  Coverage          77.37%   77.37%           
==============================================
  Files                164      164           
  Lines              14459    14459           
==============================================
  Hits               11187    11187           
  Misses              3272     3272           

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