[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...
This is a follow-up change to http://review.typo3.org/33392.

Releases: master, 6.2
Resolves: #52470
Change-Id: Ib3c2fa3a1a8f0e378bfa2ca4a5f6e78d1fdf3da7
Reviewed-on: http://review.typo3.org/33658
Reviewed-by: Stanislas Rolland <typo3@sjbr.ca>
Tested-by: Stanislas Rolland <typo3@sjbr.ca>