[BUGFIX] Remove leftover usage of prototype in EXT:form

Prototype is used in EXT:form, which is based on ExtJS. Prototype
was removed earlier, resulting in JavaScript errors. The broken
function calls are replaced by ExtJS pendants.

Resolves: #68391
Related: #39721
Releases: master
Change-Id: If005caa86b63cf930fc49e2408214ef4d9574c4f
Reviewed-on: http://review.typo3.org/41735


Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>