unit: revamp function signatures of unit_kill() and unit_kill_common() to omit DBusError
service: fix kill signature
socket: fix kill signature
scope, slice: kill signatures minus DBusError
dbus-*: proper use of unit_kill()
fifo-control: create fifoout - intended for use as a client FIFO to write responses into
main-no-init: unlink_control_fifo() on finish