Revert "Only register WidgetInspectorService extension in debug builds." (#22366)

This reverts commit 11350fed7f9d2088232354a131ca35a6e0aa6307.

packages/flutter/lib/src/widgets/binding.dart

@@ -323,10 +323,7 @@ abstract class WidgetsBinding extends BindingBase with SchedulerBinding, Gesture
         }
     );
 
-    assert(() {
-      WidgetInspectorService.instance.initServiceExtensions(registerServiceExtension);
-      return true;
-    }());
+    WidgetInspectorService.instance.initServiceExtensions(registerServiceExtension);
   }
 
   Future<Null> _forceRebuild() {