[BUGFIX] EXT:beuser: Fix action icon (compare user)

In EXT:beuser -> Backend User Listing there is the
possibility to add an user to the compare list.

If the user is already in the compare user list,
the user is removed from this list.

Resolves: #81079
Releases: master, 8.7
Change-Id: If0d6c132cdb2dbbd524890c3c90f92877240a284
Reviewed-on: https://review.typo3.org/52660


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>