[FEATURE] RTE: Deprecated JavaScript methods removed

This change adds documentation of breaking change #62291 which
removed some deprecated JavaScript methods of the RTE.

Releases: master
Resolves: #62291
Change-Id: I52eab4f949d8699837cb42d9bcbb64760cea1778
Reviewed-on: http://review.typo3.org/33377
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>
Reviewed-by: Stanislas Rolland <typo3@sjbr.ca>
Tested-by: Stanislas Rolland <typo3@sjbr.ca>