[BUGFIX] RTE maxWidth for magic images

The "maxWidth" TS config setting for RTE magic images does not work
after the change in rtehtmlarea to use FAL. Instead of the TS config
section "RTE.default.buttons" the section "RTE.buttons" is
consolidated - which is wrong.

Change-Id: I65abf958bfcab47965476b20c1265052544f7853
Resolves: #62930
Releases: master, 6.2
Reviewed-on: http://review.typo3.org/34102
Reviewed-by: Stanislas Rolland <typo3@sjbr.ca>
Tested-by: Stanislas Rolland <typo3@sjbr.ca>
(cherry picked from commit e396bb4a63e76de1b268739c2c850ed985403008)
Reviewed-on: http://review.typo3.org/34294