wlan: use the provided nvs fle in case no MAC address is found

Currently, wl1271-nvs.bin is not created in case /efs/imei/.nvmac.info
is not found. This breaks WiFi for the users who lost the content
of their /efs unless either one of the mentioned files is manually created.

The creation of wl1271-nvs.bin.orig is intentionally omitted.
proprietary-files.txt: remove unused firmware file