brcmfmac: remove two obsolete structure definitions

The structures brcmf_cfg80211_dev and brcmf_cfg80211_iface are only
adding complexity and provide no additional value. These have been
removed in this patch.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>