drm/i915: Remove misleading comment around bind_to_vm

It's true that we might need to context switch, but both the signalling
and implementation of the same are a few source files away. Remove it.
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -4197,10 +4197,6 @@ i915_gem_object_do_pin(struct drm_i915_gem_object *obj,
 
 	bound = vma ? vma->bound : 0;
 	if (vma == NULL || !drm_mm_node_allocated(&vma->node)) {
-		/* In true PPGTT, bind has possibly changed PDEs, which
-		 * means we must do a context switch before the GPU can
-		 * accurately read some of the VMAs.
-		 */
 		vma = i915_gem_object_bind_to_vm(obj, vm, ggtt_view, alignment,
 						 flags);
 		if (IS_ERR(vma))