Remove references to GPL since we now use a different license

[jmitrevs]

Description

Remove comments that refer to the GPL, since we now use a different license (and specify it globally)

Type of change

• [x] Other (Specify)

Tests

Just removed comments, so no new tests are needed

Checklist

• [x] I have read the guidelines for contributing.
• [x] My changes generate no new warnings.
• [x] I have installed and run pre-commit on the files I edited or added.
• [x] I have added tests that prove my fix is effective or that my feature works.

[jmitrevs]

Not sure I understand why there is the the test-sphinx/build failure.