staging: brcm80211: delete empty brcmfmac/README file

brcm80211/brcmfmac/README contents were move to brcm80211/README previously,
but this empty file is still around.

Signed-off-by: Henry Ptasinski <henryp@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>