Don't remove DistillabilityService on RenderFrameHost switch

If the RenderFrameHost is swapped, it usually means the old host will
be destroyed. Manual cleanup of the mojo service should not be
necessary since the attached interfaces will be removed during
destruction.

BUG=624260

Review-Url: https://codereview.chromium.org/2185733002
Cr-Commit-Position: refs/heads/master@{#408244}

components/dom_distiller/content/browser/distillability_driver.cc

@@ -85,10 +85,6 @@ void DistillabilityDriver::RenderFrameHostChanged(
   // or from a native page), the service needs to be attached to that host.
   mojo_needs_setup_ = true;
   SetupMojoService(new_host);
-  // Clean up the service on the old host if possible.
-  if (!old_host || !old_host->GetInterfaceRegistry()) return;
-  old_host->GetInterfaceRegistry()
-      ->RemoveInterface<mojom::DistillabilityService>();
 }
 
 void DistillabilityDriver::DidStartProvisionalLoadForFrame(