Delete useless JS::Value forward declaration.

ProfileViewer.h forward-declares JS::Value but doesn't use it. Starting
in SM68, JS::Value is a union, and this breaks at compilation.

Last modified in c02a7e1a7b, useless since 2af94c5898

Differential Revision: https://code.wildfiregames.com/D3102
This was SVN commit r24186.

source/ps/ProfileViewer.h

@@ -28,11 +28,6 @@
 
 class ScriptInterface;
 
-namespace JS
-{
-	class Value;
-}
-
 /**
  * Struct ProfileColumn: Describes one column of an AbstractProfileTable.
  */