svcmgr: don't send reply to one-way txn (part deux)

Do not split transaction into two when sending synchronous responses.

Partially revert changes associated with binder_send_reply from
previous incantations in commit 51f592c7
that resulted in a performance regression.

Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 27111612
Bug: 28696050
Bug: 28946245
Change-Id: I12edc10a2d1408a71507a7983afa7f17b5a6a81b