Breaking: #77345 - EXT:form - Remove deprecated IMAGEBUTTON element

See forge#77345

Description

The IMAGEBUTTON element has been removed in TYPO3 v8.

Impact

Using the IMAGEBUTTON element is not working anymore, i.e. no IMAGEBUTTON element will be rendered.

Affected Installations

All installations using the IMAGEBUTTON element.

Migration

Remove all usages of the IMAGEBUTTON element.