brcmfmac: remove unused event related definitions

The driver had some global definitions in dhd.h to map event
identifiers to event names. With redesign of firmware event
processing this has all moved to fweh module so these definitions
can be removed.

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