co2_sensor: Remove state 'INVALID'

Ongoing investigation showed that the sensor
does report 0 ppm only after startup, i.e.
in 'BOOTUP' state. We check for this condition
in `hasSensprSettled()` already, so there is no
need for this state anymore.
1 job for dev/fixstartup in 1 minute and 39 seconds (queued for 1 minute and 2 seconds)
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