Clean up onCommunicationDeviceChanged callback logic

Minor clean up for the recently added onCommunicationDeviceChanged
callback that is being used to listen to changes to the communication
device (only being used for speaker right now). Ensure that we only send
SPEAKER_ON when the current audio route isn't in speaker. Also, remove
the condition check on sending SPEAKER_OFF when the original pending
audio route is speaker. Considering a case where we switch from speaker
-> BT -> earpiece, we will wait for the following pending messages:
SPEAKER_OFF, BT_AUDIO_CONNECTED, BT_AUDIO_DISCONNECTED. If these
requests happen quickly and depending on when we receive the
onCommunicationDeviceChanged callback update for speaker, it might be
possible that we would've already processed the request to switch to
earpiece. In this case, the pending original route would be updated from
speaker to BT so when we do receive the update from the callback, we
wouldn't send the SPEAKER_OFF msg (inadvertently leaving the speakerphone
icon on in the notification bar).

Bug: 375473325
Test: Manual
Flag: EXEMPT bugfix
Change-Id: I98ac1376b5e1cb862fd1db748358071fb517d46a