Btrfs: incremental send, remove dead code

Btrfs: incremental send, remove dead code

The logic to detect path loops when attempting to apply a pending
directory rename, introduced in commit
f959492fc15b (Btrfs: send, fix more issues related to directory renames)
is no longer needed, and the respective fstests test case for that commit,
btrfs/045, now passes without this code (as well as all the other test
cases for send/receive).

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
(cherry picked from commit 5f806c3ae2ff6263a10a6901f97abb74dac03d36)