Fix performance regression caused by the new scheduler changes (#422)

* Call interrupt less often, remove some leftovers from the old scheduler code

* Remove unneeded attribute

Ryujinx.HLE/HOS/Kernel/SvcThread.cs

@@ -81,8 +81,6 @@ namespace Ryujinx.HLE.HOS.Kernel
             CurrentThread.Exit();
 
             System.Scheduler.StopThread(CurrentThread);
-
-            System.Scheduler.CoreContexts[CurrentThread.CurrentCore].RemoveThread(CurrentThread);
         }
 
         private void SvcSleepThread(AThreadState ThreadState)