[BUGFIX] Remove leftover reference to ext:func from Gruntfile

The ext:func module menu image building is still
referenced in the Gruntfile.

Change-Id: Iaafed19faa9d99eca2ebce41ea622ef85728eabc
Resolves: #82154
Releases: master
Reviewed-on: https://review.typo3.org/53765


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>