kernel: Replace usage of boost::intrusive_ptr with std::shared_ptr for kernel objects. (#3154)

* kernel: Replace usage of boost::intrusive_ptr with std::shared_ptr for kernel objects.

- See https://github.com/citra-emu/citra/pull/4710 for details.

src/audio_core/audio_renderer.cpp

@@ -73,7 +73,7 @@ private:
     EffectInStatus info{};
 };
 AudioRenderer::AudioRenderer(Core::Timing::CoreTiming& core_timing, AudioRendererParameter params,
-                             Kernel::SharedPtr<Kernel::WritableEvent> buffer_event,
+                             std::shared_ptr<Kernel::WritableEvent> buffer_event,
                              std::size_t instance_number)
     : worker_params{params}, buffer_event{buffer_event}, voices(params.voice_count),
       effects(params.effect_count) {