audio: make system own master gain semantics

engine/src/Audio/WindowsAudioBackend.cpp

@@ -141,22 +141,6 @@ bool WaveOutBackend::SetDevice(const std::string& deviceName) {
     return false;
 }
 
-float WaveOutBackend::GetMasterVolume() const {
-    return m_masterVolume.load();
-}
-
-void WaveOutBackend::SetMasterVolume(float volume) {
-    m_masterVolume.store(std::max(0.0f, std::min(1.0f, volume)));
-}
-
-bool WaveOutBackend::IsMuted() const {
-    return m_muted.load();
-}
-
-void WaveOutBackend::SetMuted(bool muted) {
-    m_muted.store(muted);
-}
-
 void WaveOutBackend::Start() {
     if (m_isRunning.load()) {
         return;
@@ -309,7 +293,7 @@ void WaveOutBackend::AudioThread() {
             continue;
         }
 
-        FillPcm16Buffer(*targetBuffer, m_pendingMixBuffer, m_masterVolume.load(), m_muted.load());
+        FillPcm16Buffer(*targetBuffer, m_pendingMixBuffer);
         m_hasPendingMix = false;
         lock.unlock();