selftests/mm: remove PROT_EXEC req from file-collapse tests

selftests/mm: remove PROT_EXEC req from file-collapse tests

As of v6.8 commit 7fbb5e188248 ("mm: remove VM_EXEC requirement for THP
eligibility") thp collapse no longer requires file-backed mappings be
created with PROT_EXEC.

Remove the overly-strict dependency from thp collapse tests so we test the
least-strict requirement for success.

Link: https://lkml.kernel.org/r/20250909190534.512801-1-zokeefe@google.com
Signed-off-by: Zach O'Keefe <zokeefe@google.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>