mox-support: remove SDIO firmware from this package

We don't longer need to ship SDIO firmware in mox-support package as this firmware is already present in package mwifiex-sdio-firmware [1], which is located in linux-firmware's Makefile.

Package mwifiex-sdio-firmware is pulled by lists/base/min.lua.m4 and lists/kmod-mox.list from turris-build repsitory.

[1] ed381e2fb2bde3e45295dff46f5fd8ca2e2c51b9 ("linux-firmware: add support for Marvell SDIO 8997")