Kernel: Remove Thread::wait_objects_index and use wait_objects to hold all the objects that a thread is waiting on.

src/core/hle/kernel/thread.cpp

@@ -579,6 +579,11 @@ void Thread::SetWaitSynchronizationOutput(s32 output) {
     context.cpu_registers[1] = output;
 }
 
+s32 Thread::GetWaitObjectIndex(WaitObject* object) const {
+    auto match = std::find(wait_objects.rbegin(), wait_objects.rend(), object);
+    return std::distance(match, wait_objects.rend()) - 1;
+}
+
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 void ThreadingInit() {