firmware-shift-sdm845: use new hexagonrpcd paths and use upstream wifi firmware

Adjust the sensor firmware paths for hexagonrpcd 0.3.1.

Also drop board-2.bin file which is now upstream and use upstream mba.mbn and wlanmdsp.mbn.

This is split from !5099 (merged) because both wifi and sensor related changes need to go together for this one. Sensors work, but wifi breaks. So this needs further testing from device maintainers/users. I don't have a shift6mq device to debug it myself. So I m gonna RFT here.