bluetooth/bluez5-util: Do not reply to ClearConfiguration

Similar to the situation/comment in `endpoint_release` BlueZ does not
request any reply to `ClearConfiguration()` either; sending one results
in the same "0 matched rules" warning from dbus-daemon:

    dbus-daemon[1309]: [system] Rejected send message, 0 matched rules; type="method_return", sender=":1.71" (uid=1000 pid=87548 comm="../build/src/daemon/pulseaudio -vvvv -n -F ../buil") interface="(unset)" member="(unset)" error name="(unset)" requested_reply="0" destination=":1.3" (uid=0 pid=1308 comm="/usr/lib/bluetooth/bluetoothd -d ")

Solve this by only creating a return message when an (othwise empty)
reply is solicited for, just like in `endpoint_release`.

Unfortunately we also have to make sure to not send any error back if no
reply is requested, but fortunately an argument parsing error here is
extremely unlikely.

Part-of: <pulseaudio/pulseaudio!472>