multimedia/handbrake: update to 1.3.1

1. remove patch-gtk_src_Makefile.am This patch has already been merged by upstream.

2. update ffmpeg to 4.2.2 in CONTRIB_FILES. Upstream has updated to this version.

3. update 'version.txt' Picked from released source archive.

PR: 243114
Submitted by: naito.yuichiro@gmail.com (maintainer)
MFH: 2020Q1