logger: avoid setting the interval for topics where not needed
logger: avoid setting the interval for topics where not needed

Saves some RAM, although not much in that case. But all subscriptions
combined need ~1.5KB only for the interval data within uORB.

dagar/Firmware,jlecoeur/Firmware,PX4/Firmware,jlecoeur/Firmware,mcgill-robotics/Firmware,acfloria/Firmware,mcgill-robotics/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,PX4/Firmware,PX4/Firmware,acfloria/Firmware,jlecoeur/Firmware,mcgill-robotics/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,dagar/Firmware,Aerotenna/Firmware,dagar/Firmware,PX4/Firmware,mcgill-robotics/Firmware,krbeverx/Firmware,mcgill-robotics/Firmware,Aerotenna/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,dagar/Firmware,krbeverx/Firmware,krbeverx/Firmware,mcgill-robotics/Firmware,dagar/Firmware,jlecoeur/Firmware,Aerotenna/Firmware,dagar/Firmware,Aerotenna/Firmware,jlecoeur/Firmware,acfloria/Firmware,Aerotenna/Firmware,jlecoeur/Firmware,dagar/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,jlecoeur/Firmware,acfloria/Firmware,mcgill-robotics/Firmware,jlecoeur/Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware,Aerotenna/Firmware,Aerotenna/Firmware,acfloria/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,PX4/Firmware