fdo#75757: remove inheritance to std::vector

from SfxVerbSlotArr_Impl.

Change-Id: I84582f10095638a0fef82aa46f721d57a8b27c27
Reviewed-on: https://gerrit.libreoffice.org/11662
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>