[FOLLOWUP][TASK] Get rid of clear.gif in buttons

Type image without src attribute is not allowed.
Use type submit instead.

Resolves: #68304
Releases: master
Change-Id: I3e85595f6320c3057a59309fe391a02fcfe43744
Reviewed-on: http://review.typo3.org/42293


Reviewed-by: Frank Nägler <frank.naegler@typo3.org>
Tested-by: Frank Nägler <frank.naegler@typo3.org>