drm/i915: Delete defunct i915_gem_request_assign()

i915_gem_request_assign() is not used since commit 77f0d0e9
("drm/i915/execlists: Pack the count into the low bits of the
port.request"), so remove the defunct code

References: 77f0d0e9 ("drm/i915/execlists: Pack the count into the low bits of the port.request")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180102151235.3949-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_request.h

@@ -245,18 +245,6 @@ i915_gem_request_put(struct drm_i915_gem_request *req)
 	dma_fence_put(&req->fence);
 }
 
-static inline void i915_gem_request_assign(struct drm_i915_gem_request **pdst,
-					   struct drm_i915_gem_request *src)
-{
-	if (src)
-		i915_gem_request_get(src);
-
-	if (*pdst)
-		i915_gem_request_put(*pdst);
-
-	*pdst = src;
-}
-
 /**
  * i915_gem_request_global_seqno - report the current global seqno
  * @request - the request