Evaluated solo specific tones file vs standard px4 tones files. The
only thing the Solo had that standard ArduPilot does not have is the GPS
unplugged tone and the power off tone.
* Some tones have a different tune, which is fine. We want the Solo to
sound like ArduPilot if it is running ArduPilot.
* GPS unplugged tone abandoned. Determined to be unnecessary.
* Power off tone merged into standard px4 tones file. Smart battery
signalling a power off will make use of this tone. Has application for
any smart battery equipped vehicle, not just Solo.
* Removed all references and dependencies to `ToneAlarm_PX4_Solo.cpp`
and `ToneAlarm_PX4_Solo.h`
* Deleted `ToneAlarm_PX4_Solo.cpp` and `ToneAlarm_PX4_Solo.h` since
they're no longer needed.
Due to the way the headers are organized changing a single change in
an AP_Notify driver would trigger a rebuild for most of the files in
the project. Time could be saved by using ccache (since most of the
things didn't change) but we can do better, i.e. re-organize the headers
so we don't have to re-build everything.