remove old api

Author: hyperblast

src/Client/SetPlayerStateRequest.cs

@@ -22,11 +22,6 @@ public sealed class SetPlayerStateRequest
     /// </remarks>
     public double? RelativeVolume { get; set; }
 
-    /// <summary>
-    /// Adjust volume in one step: 1 for volume increase, -1 for volume decrease.
-    /// </summary>
-    public int? VolumeStep { get; set; }
-
     /// <summary>
     /// New mute state.
     /// </summary>