Avoid infinite generics recursion in SynchronizationContextScheduler

The infinitive generics recursion interacts poorly with AOT. The AOT compilers have hard figuring
out where the stop generating the code for generics with infinite recursion. They either fail or
produce large images by giving up once the generics get too complex.

This change reverts a small part of dotnet#500 that introduced infinite generic recusion and adds comment.

Fixes dotnet/corert#7920

Rx.NET/Source/src/System.Reactive/Concurrency/SynchronizationContextScheduler.cs

@@ -93,7 +93,8 @@ public override IDisposable Schedule<TState>(TState state, TimeSpan dueTime, Fun
                 return Schedule(state, action);
             }
 
-            return DefaultScheduler.Instance.Schedule((scheduler: this, action, state), dt, (_, tuple) => tuple.scheduler.Schedule(tuple.state, tuple.action));
+            // Note that avoiding closure allocation here would introduce infinite generic recursion over the TState argument
+            return DefaultScheduler.Instance.Schedule(state, dt, (_, state1) => Schedule(state1, action));
         }
     }
 }