vd_d3d11vpp: remove nonsensical flush call

I made this call up because I sort of thought this makes senssssse. I'm
now convinced that it does not, and even is actively harmful. I'm still
quite in the dark how the DirectD 11 video API is supposed to work with
synchronization, but at least for normal graphics this call would not
make much sense.

video/filter/vf_d3d11vpp.c

@@ -331,11 +331,6 @@ static int render(struct vf_instance *vf)
         goto cleanup;
     }
 
-    // Make sure the texture is updated correctly on the shared context.
-    // (I'm not sure if this is correct, though it won't harm.)
-    if (p->out_shared)
-        ID3D11DeviceContext_Flush(p->device_ctx);
-
     res = 0;
 cleanup:
     if (in_view)