s390/Kconfig: drop superfluous "select SPARSEMEM_VMEMMAP"

s390/Kconfig: drop superfluous "select SPARSEMEM_VMEMMAP"

Now handled by the core automatically once SPARSEMEM_VMEMMAP_ENABLE is
selected.

Link: https://lkml.kernel.org/r/20250901150359.867252-4-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>