docker: fedora: update to Fedora 31

aom-extra-tools has been removed from Fedora:
038d7b2164

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.

docker/fedora/Dockerfile

@@ -1,4 +1,4 @@
-FROM registry.fedoraproject.org/fedora:30
+FROM registry.fedoraproject.org/fedora:31
 
 ENV RUSTUP_HOME=/usr/local/rustup \
     CARGO_HOME=/usr/local/cargo \

docker/fedora/prepare.sh

@@ -1,6 +1,6 @@
 set -eux
 
-dnf install -y git-core ninja-build dnf-plugins-core
+dnf install -y git-core ninja-build dnf-plugins-core python3-pip
 
 # Configure git for various usage
 git config --global user.email "gst-build@gstreamer.net"
@@ -17,7 +17,6 @@ dnf upgrade -y
 dnf install -y \
     aalib-devel \
     aom \
-    aom-extra-tools \
     bat \
     libaom \
     libaom-devel \
@@ -41,6 +40,7 @@ dnf install -y \
     graphene-devel \
     gsl \
     gsl-devel \
+    faac-devel \
     ffmpeg \
     ffmpeg-libs \
     ffmpeg-devel \
@@ -180,7 +180,6 @@ dnf builddep -y gstreamer1 \
     gstreamer1-plugins-good-extras \
     gstreamer1-plugins-ugly \
     gstreamer1-plugins-ugly-free \
-    gstreamer1-plugins-bad-nonfree \
     gstreamer1-plugins-bad-free \
     gstreamer1-plugins-bad-free-extras \
     gstreamer1-plugins-bad-freeworld \