Revert "Merge commit '3bc2e89c'" (Bump libavutil major version to account for the LLS API/ABI changes.)

This reverts commit 792845e4, reversing
changes made to 1d6666a6.

Bumping libavutil requires all libraries that use libavutil to have their
major version bumped (yes breakage has been confirmed this is not a hypotheses)

One case of breakage is due to new types being added to AVOptions and
applications that linked to old libavutil and libswresample
then trying to use old libavutil (its soname changed so the old isnt updated)
and new swresample (its soame didnt change so it is updated)
the new swresample contains AVOption types that the old libavutil doesnt
know of thus the application attempting to access these avoptions
fails

AVOptions are used by all libs so the issue can potentially happen with
any other lib, libswresample was just the first that showed the problem
ive not checked if the other libs are affected currently by the same issue
or not

Also in addition to AVOptions, AVFrames are also defined in
libavutil, bumping it without all libs that use AVFrames could lead to
serious inconsistencies when 2 libs/app end up using 2 different libavutils

The alternative of bumping all is still possible after this revert, if it
turns out to be the preferred solution