[BUGFIX] Remove legacy TCA related to Variant

The concept "Variant" has been removed as of Media 3.0
since CMS 6.2 provides all the necessary mechanism
by default e.g. image within the RTE are now handled
as Processed Image which was one of the reason of the Variant.

Also another idea behind Variant was the possibility
to create connection between files. The same could be achieved
by File References.

Change-Id: I29fd4c2eea9bd1355cc59b4ab82719ffbbed6efd
Releases: 3.0
Resolves: #58737
Reviewed-on: https://review.typo3.org/30031
Reviewed-by: Fabien Udriot
Tested-by: Fabien Udriot