We have all these stubs that only exist because they're called from
btrfs_run_sanity_tests, which is a static inside super.c.  Let's just
move it all into tests/btrfs-tests.c and only have one stub.
Signed-off-by: NJeff Mahoney <jeffm@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>