audio_manager: Remove dependence on system state

This isn't used by the class, so this can be removed for the time being.

src/audio_core/audio_manager.cpp

@@ -8,7 +8,7 @@
 
 namespace AudioCore {
 
-AudioManager::AudioManager(Core::System& system_) : system{system_} {
+AudioManager::AudioManager() {
     thread = std::jthread([this]() { ThreadFunc(); });
 }