Use binder rather than kernel ONEWAY flag.

FLAG_ONEWAY is defined by IBinder, but TF_ONE_WAY is defined by the
binder kernel. These both have the value '1'.

In order to remove the binder kernel headers as an export of libbinder,
FLAG_ONEWAY should be used.

Bug: 124524556
Test: N/A
Change-Id: If71673b3bd4f41e34316c39e2139a9e39912dd23