[TASK] EM: Fix icon leftovers

The "Update extension" task uses an FA icon now. The obsolete file
"ExtensionUpdateScript.png" is removed.

Resolves: #65500
Releases: master
Change-Id: If527b0e8fd77a059c8b25db16a926c5c80356331
Reviewed-on: http://review.typo3.org/37514


Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>