brcmsmac: Remove unused wlc_prio2prec_map and _BRCMS_PREC_* constants

Fixes sparse warning:
drivers/net/wireless/brcm80211/brcmsmac/main.c:308:10: sparse: symbol 'wlc_prio2prec_map' was not declared. Should it be static?

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>