CRAS: rstream - Remove unused flags variable.

After three years we haven't found a use for flags, remove it.

BUG=none
TEST=make check

Change-Id: I4a3e7af0c23a27d5fedac8f3a21bd5d7aa6580da
Signed-off-by: Dylan Reid <dgreid@chromium.org>
CRAS: rstream - re-order struct

To keep the input/output shm variables together, put the format and
list members at the bottom.  Add a comment describing the members.

BUG=none
TEST=none

Change-Id: If2ea9d1cff4b8dc7bec45aee0dd3b0beb453ac6b
Signed-off-by: Dylan Reid <dgreid@chromium.org>