Remove code for Firefox bug 1313937

Problem/Motivation

Firefox had a bug that would not respect 'strict-dynamic', nonces, or hashes set on default-src if it was a fallback for script-src or style-src that were not set on a policy. (https://bugzilla.mozilla.org/show_bug.cgi?id=1313937).

CSP module addresses this by copying the default-src value to the other directives if necessary.

The bug was fixed in Firefox 117 (Released Aug 2023, End of support Sep 2023), but is still present in the ESR 115 release supported until Oct 2024.

Proposed resolution

After Oct 2024, remove the Firefox bug fix method

Remaining tasks

User interface changes

API changes

Data model changes