stream_session: remove duplicated debug message
stream_session: remove duplicated debug message

Whenever we call get_session, that will print a debug message about the arrival
of this new verb. Because we also print that explicitly in PREPARE_DONE, that
message gets duplicated.

That confuses poor developers who are, for a while, left wondering why is it that
the sender is sender the message twice.

Signed-off-by: Glauber Costa <7ba9037b0dd006f9408bd45b94707becd5cd4e87@scylladb.com>

scylladb/scylla,kjniemi/scylla,scylladb/scylla,raphaelsc/scylla,kjniemi/scylla,scylladb/scylla,raphaelsc/scylla,duarten/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,duarten/scylla,duarten/scylla,raphaelsc/scylla,kjniemi/scylla