ipq-wifi: drop custom board-2.bins

ipq-wifi: drop custom board-2.bins

The BDFs for all boards were upstreamed to the ath10k-firmware
repository and are now part of ath10k-firmware 2018-04-19.

We switched to the upstream board-2.bin, hence the files can be removed
here.

Keep the ipq-wifi package in case new boards are added. It might take
some time till board-2.bins send upstream are merged.

Signed-off-by: Sven Eckelmann <sven.eckelmann@openmesh.com>