ffmpeg: update to version 4.2.5

Compile and run tested on Turris 1.1, powerpc8540

Remove PKG_MAINTAINER line as this package is in our repository and thus we maintain it. Also, this version was not in OpenWrt. There is a newer version for OpenWrt 21.02+

changed milestone to %Turris OS 5.3.0

added Package update label

requested review from @mvasilek

assigned to @mvasilek

approved this merge request

assigned to @jschlehofer and unassigned @mvasilek

requested review from @jschlehofer and removed review request for @mvasilek

added 4 commits

• 4234abcc...c04d55b0 - 3 commits from branch master
• 7459ce12 - ffmpeg: update to version 4.2.5

Compare with previous version

merged

changed milestone to %Turris OS 5.3.1