Even though it hasn't been supported forever, the files where still
being compiled

Prevent shutdown ordering crashes

PX4 doesn't retry commands by default

Also changed GPS FactGroup values to use NaN appropriately to show
unavailable values.

No need to add dynamic MockLink comm links

altitudeAMSL and altitudeRelative do not need divide 1000，the unit is meter and float format。 can you use _handleGlobalPositionInt message for altitudeAMSL and altitudeRelative？ because _handleGlobalPositionInt is default 5Hz and _handleAltitude is 1Hz.

It's not desired to have automatic log streaming for several reasons:
- There's already SD logging (which is the case for the majority of the
  users)
- The link does not provide the necessary bandwidth (eg. wireless telemetry)