[TASK] Removes useless icon used in BE login template

In the backend login template there is an old logo which
is not used anymore. We can remove it.

Resolves: #61963
Releases: master
Change-Id: I18ad8d1b57a8c0ca8223ac89a356f5b93370645c
Reviewed-on: http://review.typo3.org/33079
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>