Windows 7/8 and Mac 10.12-10.14 EOL update

[Ryan VanderMeulen]

Hello, as you are probably aware, we recently began the process of migrating users on Windows 7/8/8.1 and macOS 10.12-10.14 to the ESR115 release in support of their recently-announced EOLs [1][2]. However, there was a bit of a hold-up in our ability to begin cleaning up the codebase due to some CI migration work which needed to be completed first.

I'm sending this out to confirm that all of the necessary work blocking the code cleanup is now complete. Code that was only needed to support those older OS releases is now safe to remove from mozilla-central. If you're looking for meta bugs to hang your work off, bug 1594270 can be used for Windows and bug 1836375 for macOS.

Thanks for your patience!

-Ryan

[1] https://blog.mozilla.org/futurereleases/2023/07/06/firefox-support-for-macos-10-12-10-13-and-10-14/

[2] https://blog.mozilla.org/futurereleases/2023/07/06/firefox-support-for-windows-7-8-and-8-1/