Issue #2976889 by phenaproxima, xjm, chr.fritsch, samuel.mortenson, larowlan, alexpott: Add a trait to create media types in tests and replace MediaFunctionalTestCreateMediaTypeTrait

Revert "Issue #2976889 by phenaproxima, xjm, samuel.mortenson, chr.fritsch: Add a trait to create media types in tests and replace MediaFunctionalTestCreateMediaTypeTrait"

This reverts commit 58d601eb.

Issue #2976889 by phenaproxima, xjm, samuel.mortenson, chr.fritsch: Add a trait to create media types in tests and replace MediaFunctionalTestCreateMediaTypeTrait

Issue #2883813 by chr.fritsch, Wim Leers, Berdir, phenaproxima, catch: Move File/Image media type into Standard once Media is stable

Issue #2895581 by chr.fritsch, Wim Leers: Add test coverage ensuring that the media source field cannot be removed from a media type

Issue #2894270 by xjm, seanB, chr.fritsch, Wim Leers: Users unable to add an extension to the file upload field