Remove dav1d-debian-experimental

It hasn't been used in over 2 years.

dav1d-debian-experimental/Dockerfile

-FROM debian:experimental-20220418
-
-MAINTAINER VideoLAN roots <roots@videolan.org>
-
-ENV IMAGE_DATE=202204221700
-
-# If someone wants to use VideoLAN docker images on a local machine and does
-# not want to be disturbed by the videolan user, we should not take an uid/gid
-# in the user range of main distributions, which means:
-# - Debian based: <1000
-# - RPM based: <500 (CentOS, RedHat, etc.)
-ARG VIDEOLAN_UID=499
-
-RUN addgroup --quiet --gid ${VIDEOLAN_UID} videolan && \
-    adduser --quiet --uid ${VIDEOLAN_UID} --ingroup videolan videolan && \
-    echo "videolan:videolan" | chpasswd && \
-    apt-get update && \
-    apt-get -y dist-upgrade && \
-    apt-get install --no-install-suggests --no-install-recommends -y -t experimental \
-        build-essential gcc clang && \
-    apt-get install --no-install-suggests --no-install-recommends -y \
-        ca-certificates curl git python3-pip \
-        python3-setuptools python3-wheel nasm mold && \
-    pip3 install meson ninja && \
-    apt-get clean -y && rm -rf /var/lib/apt/lists/*
-
-USER videolan