tracker-extract-mp3: Use nmm:length instead of nmm:duration
tracker-extract-mp3: Use nmm:length instead of nmm:duration

nmm:duration is not defined in the ontology.

hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,hoheinzollern/tracker