Remove the SmoothScrollJSIntervention runtime enabled flag

It has been on stable for quite a while now.

Change-Id: Ibe06fc8ad4e36d7ce070cfb40c7ad01ae72adc36
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1766783Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690438}

third_party/blink/renderer/core/dom/events/event_target.cc

@@ -388,8 +388,7 @@ void EventTarget::SetDefaultAddEventListenerOptions(
   // For mousewheel event listeners that have the target as the window and
   // a bound function name of "ssc_wheel" treat and no passive value default
   // passive to true. See crbug.com/501568.
-  if (RuntimeEnabledFeatures::SmoothScrollJSInterventionEnabled() &&
-      event_type == event_type_names::kMousewheel && ToLocalDOMWindow() &&
+  if (event_type == event_type_names::kMousewheel && ToLocalDOMWindow() &&
       event_listener && !options->hasPassive()) {
     JSBasedEventListener* v8_listener =
         DynamicTo<JSBasedEventListener>(event_listener);

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -1519,10 +1519,6 @@
       name: "SkipTouchEventFilter",
       settable_from_internals: true,
     },
-    {
-      name: "SmoothScrollJSIntervention",
-      status: "stable",
-    },
     {
       name: "SmsReceiver",
       status: {"Android": "experimental", "default": "test"},