Revert "Adding support for the .NET scripting background"

This reverts commit 676967d.

Author: wiwei

Assets/MixedRealityToolkit/Attributes/MixedRealityExtensionServiceAttribute.cs

@@ -71,17 +71,12 @@ public MixedRealityExtensionServiceAttribute(
             PackageFolder = packageFolder;
         }
 
-#if UNITY_EDITOR
         /// <summary>
         /// Convenience function for retrieving the attribute given a certain class type.
         /// </summary>
-        /// <remarks>
-        /// This function is only available in a UnityEditor context.
-        /// </remarks>
         public static MixedRealityExtensionServiceAttribute Find(Type type)
         {
             return type.GetCustomAttributes(typeof(MixedRealityExtensionServiceAttribute), true).FirstOrDefault() as MixedRealityExtensionServiceAttribute;
         }
-#endif // UNITY_EDITOR
     }
 }