transport: revert bug added in 6a53cbe

This patch reverts the commit 6a53cbe
("thorium: prepare message in transport").

The transport does not know about actors, it only send messages
(count, buffer, source node, destination node). In theory, the
preparation of received messages should work inside the
transport subsystem. But it does not.

On Beagle (Cray XE6), this error is generated:

Assertion failed in file
/notbackedup/tmp/ulib/mpt/nightly/6.0/081313/mpich2/src/mpi/datatype/get_count.c
at line 34: size >= 0 && status->count >= 0

This patch restores the old code path (which works fine).

Link: https://github.com/GeneAssembly/biosal/issues/774
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>