Upgrade to 4.3.1-1 and use system opusenc

This upgrades the package to musescore version 4.3.1, removes a seemingly unnecessary cherry-pick (the commit's change seems to be included in the used tag) and updates the PKGBUILD to use the system opusenc library. This final change fixes #4 . Because these changes are small and partially dependent on one another, I did not create a MR for each but instead created a commit for each modification. If necessary, I can of course still handle this in a different way.