drm/i915/guc: drop guc_communication_enabled

The function is only used from within GEM_BUG_ON(), which is causing
warnings with Wunneeded-internal-declaration in some builds. Since the
function is a simple wrapper around a CT function, we can just call the
CT function directly instead.

Fixes: 1fb12c58

 ("drm/i915/guc: skip disabling CTBs before sanitizing the GuC")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210823163137.19770-1-daniele.ceraolospurio@intel.com