[!!!][TASK] Remove mediace from the Core

The EXT:mediace is now available on TER and GitHub
for further development and is removed from the
Core. An upgrade wizard checks the instance for
usage of plugins of ext:mediace. If found an
upgrade wizard is provided that offers to
activate the extension.

Resolves: #68079
Resolves: #71082
Releases: master
Change-Id: I07c15a9b76013e2e5f3db7e3e6469fe48a25270a
Reviewed-on: https://review.typo3.org/41135


Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>