For some reason we unlock everything except the leaf we are on, set the path
blocking and then add the extent item for the extent we just finished
writing.  I can't for the life of me figure out why we would want to do
this, and the history doesn't really indicate that there was a real reason
for it, so just remove it.  This will reduce our tree lock contention on
heavy writes.  Thanks,
Signed-off-by: Josef Bacik <jbacik@fusionio.com>