wireguard: selftests: remove CONFIG_SPARSEMEM_VMEMMAP=y from qemu kernel config

wireguard: selftests: remove CONFIG_SPARSEMEM_VMEMMAP=y from qemu kernel config

It's no longer user-selectable (and the default was already "y"), so let's
just drop it.

It was never really relevant to the wireguard selftests either way.

Link: https://lkml.kernel.org/r/20250901150359.867252-6-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-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: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>