[FOLLOWUP][BUGFIX] Exchange flag icons from SVG to PNG

Remove flag SVG's from grunt and bower.

Resolves: #76291
Releases: master
Change-Id: I5698c5b23e74848a0330f080845d1d471ac37523
Reviewed-on: https://review.typo3.org/53019


Reviewed-by: Mona Muzaffar <mona.muzaffar@gmx.de>
Tested-by: Mona Muzaffar <mona.muzaffar@gmx.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>