drm/i915/guc: Drop comment on fwif autogeneration

The firmware interface file was initially partially autogenerated, but
this is no longer the case.

It was never updated automatically, and a lot manual changes were
introduced since.

>From now on any changes to the firmware interface will be managed by
hand, which gives us flexibility when it comes to structure reuse
(HuC/GuC) and naming conventions.

Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Cc: Jeff Mcgee <jeff.mcgee@intel.com>
Cc: Sagar A. Kamble <sagar.a.kamble@intel.com>
Signed-off-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Reviewed-by: Jeff McGee <jeff.mcgee@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1480953869-25267-1-git-send-email-arkadiusz.hiler@intel.com