mwan3: remove notracking in mwan3track ubus status

mwan3: remove notracking in mwan3track ubus status

The function 'get_mwan3_status' is reading the internal state from the
tracker via the status file. Do not use the state 'notracking' status
anymore. If the mwan3track is not running always return 'unknown'
and not 'notracking'. There is already an other function that evaluates
the external state of the tracker.

We have now the following states of the tracker:
internal (mwan3track):
- offline
- online
- diconnecting
- connecting
- disabled
- unknown

external (via pgrep and config):
- paused
- active
- down
- not enabled

Signed-off-by: Florian Eckert <fe@dev.tdt.de>