Remove unnecessary include

Author: KoraLyn

xivModdingFramework/Materials/FileTypes/Mtrl.cs

@@ -14,7 +14,6 @@
 // You should have received a copy of the GNU General Public License
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-using HelixToolkit.SharpDX.Core;
 using SharpDX;
 using System;
 using System.Collections.Generic;