The only place the trans_info->alloc list is used is when
initializing it, when adding a transaction to it when allocation
finishes, and when moving a transaction from that list to the
committed list.

We can just skip putting a transaction on the allocated list, and
add it (rather than move it) to the committed list when it is
committed.

On additional caveat is that an allocated transaction that's
committed without any TREs added will be immediately freed.  Because
we aren't adding allocated transactions to a list any more, the
list links need to be initialized to ensure they're valid at the
time list_del() is called for the transaction.

Then we can safely eliminate the allocated transaction list.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>