fstests: Use _require_scratch_dax_mountopt() and _require_dax_iflag()

1) Make related tests use _require_scratch_dax_mountopt() and _require_dax_iflag().
2) Remove unused _require_scratch_dax().

Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>
6 files changed