selftests/vm: drop mnt point for hugetlb in run_vmtests.sh

After converting all the three relevant testcases (uffd, madvise, mremap)
to use memfd, no test will need the hugetlb mount point anymore.  Drop the
code.

Link: https://lkml.kernel.org/r/20221014144015.94039-1-peterx@redhat.com


Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>