docker: fedora: update to Fedora 31

docker: fedora: update to Fedora 31

aom-extra-tools has been removed from Fedora:
https://src.fedoraproject.org/rpms/aom/c/038d7b2164e15c9067af3d2d2e0b50a4d890b218?branch=master

gstreamer1-plugins-bad-nonfree has been removed from rpmfusion:
https://pkgs.rpmfusion.org/cgit/nonfree/gstreamer1-plugins-bad-nonfree.git/commit/?id=30641c2ded63d12e099d32cb814bab8244f48c90
It was only used of its build deps of which only faac-devel was not
already installed, so I added it instead.

Need to manually install pip3 now.