Revert "syscallarg_t: Add a type for system call arguments"
Missed issues in truss on at least armv7 and powerpcspe need to be
resolved before recommit.
This reverts commit 3889fb8af0b611e3126dc250ebffb01805152104.
This reverts commit 1544e0f5d1f1e3b8c10a64cb899a936976ca7ea4.