drm/xe/guc: Drop unused legacy GuC message ABI definitions

Those were copy-pasted from i915 code and never used in Xe driver.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240610120411.1768-2-michal.wajdeczko@intel.com