Btrfs: fix compiles when CONFIG_BTRFS_FS_RUN_SANITY_TESTS is off

Commit fccb84c9

 moved added some helpers to cleanup our sanity tests,
but it looks like both Dave and I always compile with the tests enabled.

This fixes things to work when they are turned off too.

Signed-off-by: Chris Mason <clm@fb.com>