Move VocLoader to Mods.D2k

While this is strictly speaking a D2 format, any
D2 mod is pretty much guaranteed to use Mods.D2k,
so this should be a good enough place to move it to.

OpenRA.Mods.D2k/AudioLoaders/VocLoader.cs

@@ -15,7 +15,7 @@ using System.IO;
 using System.Linq;
 using OpenRA.Primitives;
 
-namespace OpenRA.Mods.Common.AudioLoaders
+namespace OpenRA.Mods.D2k.AudioLoaders
 {
 	public class VocLoader : ISoundLoader
 	{