Revert "chromeos: disables event throttling in window-service clients"

This reverts commit 8e40f476.

Reason for revert: crbug.com/931878, touch tab-dragging gets broken

Original change's description:
> chromeos: disables event throttling in window-service clients
> 
> Only the window-service should throttle.
> 
> BUG=929914
> TEST=none
> TBR=sadrul@chromium.org
> 
> Change-Id: Iab7ea987c8fcb1f52b9c1e69576a0f950d790787
> Reviewed-on: https://chromium-review.googlesource.com/c/1470941
> Reviewed-by: Scott Violet <sky@chromium.org>
> Commit-Queue: Scott Violet <sky@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#631868}

TBR=sadrul@chromium.org,sky@chromium.org

Change-Id: I4c356212aed1cf03b6c381ef05ce404a58517351
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 929914
Reviewed-on: https://chromium-review.googlesource.com/c/1471458Reviewed-by: Jun Mukai <mukai@chromium.org>
Commit-Queue: Jun Mukai <mukai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632025}

ui/aura/env.cc

@@ -325,9 +325,6 @@ void Env::Init(service_manager::Connector* connector) {
   if (mode_ == Mode::MUS) {
     EnableMusOSExchangeDataProvider();
     EnableMusOverrideInputInjector();
-    // Remote clients should not throttle, only the window-service should
-    // throttle (which corresponds to Mode::LOCAL).
-    throttle_input_on_resize_ = false;
     return;
   }