[TASK] Remove old and unused extension icons from t3skin

in t3skin/icons/ext there are plenty of really old icons
for e.g. tt_guest or tt_calender

We should remove them as they are not used.

Resolves: #59792
Releases: 6.3
Change-Id: I8d6a91e2a1c1aa6da04ee2da961c2f6c919de2c3
Reviewed-on: http://review.typo3.org/31040
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Susanne Moog <typo3@susannemoog.de>
Tested-by: Susanne Moog <typo3@susannemoog.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>