various: remove dead api, move mixin to proper file

runelite-api/src/main/java/net/runelite/api/Client.java

@@ -1034,48 +1034,6 @@ public interface Client extends GameShell
 	 */
 	List<GraphicsObject> getGraphicsObjects();
 
-	/**
-	 * Gets the music volume
-	 *
-	 * @return volume 0-255 inclusive
-	 */
-	int getMusicVolume();
-
-	/**
-	 * Sets the music volume
-	 *
-	 * @param volume 0-255 inclusive
-	 */
-	void setMusicVolume(int volume);
-
-	/**
-	 * Gets the sound effect volume
-	 *
-	 * @return volume 0-127 inclusive
-	 */
-	int getSoundEffectVolume();
-
-	/**
-	 * Sets the sound effect volume
-	 *
-	 * @param volume 0-127 inclusive
-	 */
-	void setSoundEffectVolume(int volume);
-
-	/**
-	 * Gets the area sound effect volume
-	 *
-	 * @return volume 0-127 inclusive
-	 */
-	int getAreaSoundEffectVolume();
-
-	/**
-	 * Sets the area sound effect volume
-	 *
-	 * @param volume 0-127 inclusive
-	 */
-	void setAreaSoundEffectVolume(int volume);
-
 	/**
 	 * Play a sound effect at the player's current location. This is how UI,
 	 * and player-generated (e.g. mining, woodcutting) sound effects are