[BUGFIX] RTE: Broken context menu

RTE is not using the ExtJS registry anymore.

Releases: master
Resolves: #63785
Change-Id: I9d701062834d20c858c1043743f55e813f16dc37
Reviewed-on: http://review.typo3.org/35316
Reviewed-by: Stanislas Rolland <typo3@sjbr.ca>
Tested-by: Stanislas Rolland <typo3@sjbr.ca>