Bump Libav to v9.3.

Miscellaneous security fixes.



git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@5294 b64f7644-9d1e-0410-96f1-a4d463321fa5
decavcodec: remove unnecessary code.

Was obsolete since SVN revision 3786.



git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@5295 b64f7644-9d1e-0410-96f1-a4d463321fa5