AST: Fix compilation warning

Fix the following warning by removing the new keyword:

src/AST/Type.cs(230,25): warning CS0109: The member `CppSharp.AST.PointerType.IsReference' does not hide an inherited member. The new keyword is not required

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@iki.fi>

src/AST/Type.cs

@@ -232,7 +232,7 @@ namespace CppSharp.AST
             RVReference
         }
 
-        public new bool IsReference
+        public bool IsReference
         {
             get
             {