[FEATURE] RTE: remove deprecated JavaScript methods

Some JavaScript methods are deprecated since TYPO3 4.7.

Releases: master
Resolves: #62291
Change-Id: Ie427dc8e898233723650ebdd587e9625b8ea4419
Reviewed-on: http://review.typo3.org/33344
Reviewed-by: Stanislas Rolland <typo3@sjbr.ca>
Tested-by: Stanislas Rolland <typo3@sjbr.ca>