[mythtv] Redone FFmpeg 4.4.1

[Peter Bennett]

The code in branch devel/ffmpeg-resync is now setup in a new way.

There are a number of cleanup commits from Scott Theisen's pull request 
https://github.com/MythTV/mythtv/pull/416

After those commits there is a fresh unmodified copy of FFmpeg n4.4.1 at 
commit titled "Insert FFmpeg n4.4.1".

After that are commits that apply all of the MythTV customization. These 
are from Scott Theisen's excellent work in separating all of the 
differences into individual meaningful commits.

Then there is a commit of Klaas de Waal's fix for the blocking artifacts 
in h264 interlaced video.

Thank you to Scott and Klaas for all the work.

Please test it and see if there are any further issues.

If all is OK I will update the sync instructions, to in future use this 
method.

Before we merge back into master, I recommend that we do a rebase of 
devel/ffmpeg-resync.

If all is OK we will no longer need the MythTV/FFmpeg repository.

Peter