drm/i915: remove unused function declaration

This function is not part of the driver anymore.
Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: 90f4fcd5 ("drm/i915: Remove forced stop ring on suspend/unload")
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20170804140348.24971-1-lionel.g.landwerlin@intel.com

drivers/gpu/drm/i915/intel_lrc.h

@@ -63,7 +63,6 @@ enum {
 };
 
 /* Logical Rings */
-void intel_logical_ring_stop(struct intel_engine_cs *engine);
 void intel_logical_ring_cleanup(struct intel_engine_cs *engine);
 int logical_render_ring_init(struct intel_engine_cs *engine);
 int logical_xcs_ring_init(struct intel_engine_cs *engine);