Input: Improve Controller Interface devices threading

This specific issue was already addressed by https://github.com/dolphin-emu/dolphin/pull/11635
though I felt like there was something more we could do, and wasn't too happy with the
likelihood of devices update calls being skipped (due to `m_devices_population_mutex` being locked).

Source/Core/InputCommon/ControllerInterface/InputBackend.cpp

@@ -12,7 +12,7 @@ InputBackend::InputBackend(ControllerInterface* controller_interface)
 
 InputBackend::~InputBackend() = default;
 
-void InputBackend::UpdateInput()
+void InputBackend::UpdateInput(std::vector<std::weak_ptr<ciface::Core::Device>>& devices_to_remove)
 {
 }