[BUGFIX] RTE: In Chrome RTE inserts weird span tags

Remove the span tags inserted by Chrome or Opera on execution of
native execCommand. The attributes of these span tags have evolved...

Releases: master, 6.2
Resolves: #52470
Change-Id: Ibb046b86e869bd7d4afc61ab5005595467b288cd
Reviewed-on: http://review.typo3.org/33391
Reviewed-by: Stanislas Rolland <typo3@sjbr.ca>
Tested-by: Stanislas Rolland <typo3@sjbr.ca>