drm/i915/ctx: Remove bad invariant

It's not that the assertion is incorrect, but rather that we can call
do_destroy early in loading, and we will falsely BUG().

Since contexts have been in for a while now, and in the internal APIs
are pretty stable, it should be fairly safe to remove this.

v2: Remove unused dev_priv, and dev
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_context.c

@@ -126,13 +126,8 @@ static int get_context_size(struct drm_device *dev)
 
 static void do_destroy(struct i915_hw_context *ctx)
 {
-	struct drm_device *dev = ctx->obj->base.dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-
 	if (ctx->file_priv)
 		idr_remove(&ctx->file_priv->context_idr, ctx->id);
-	else
-		BUG_ON(ctx != dev_priv->ring[RCS].default_context);
 
 	drm_gem_object_unreference(&ctx->obj->base);
 	kfree(ctx);