xfs: fix filestreams tests when rtinherit=1

xfs: fix filestreams tests when rtinherit=1

The filestreams allocator can only be selected for files that reside on
the data volume.  In commit ee3e0010, we sprinkled calls to
_require_no_rtinherit in the filestreams tests so that there wouldn't be
regressions reported if the filesystem is formatted with -d rtinherit=1.

This unnecessarily limits test coverage because userspace can control
the device selection parameters quite easily with xfs_io chattr.  Make
the filestreams tests unset SCRATCH_RTDEV so that the allocator isn't
thrown off by the rtbitmap consuming space on the data device.

Fixes: ee3e0010 ("xfs/realtime: add _require_no_rtinherit function")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>