remove depricated extension.

src/Avalonia.OpenGL/Angle/AngleWin32EglDisplay.cs

@@ -89,7 +89,7 @@ namespace Avalonia.OpenGL.Angle
         {
             if (PlatformApi != AngleOptions.PlatformApi.DirectX11)
                 throw new InvalidOperationException("Current platform API is " + PlatformApi);
-            return egl.CreatePBufferFromClientBuffer(EGL_D3D_TEXTURE_ANGLE, handle, new[] { EGL_WIDTH, width, EGL_HEIGHT, height, EGL_FLEXIBLE_SURFACE_COMPATIBILITY_SUPPORTED_ANGLE, EGL_TRUE, EGL_TEXTURE_OFFSET_X_ANGLE, offsetX, EGL_TEXTURE_OFFSET_Y_ANGLE, offsetY, EGL_NONE });
+            return egl.CreatePBufferFromClientBuffer(EGL_D3D_TEXTURE_ANGLE, handle, new[] { EGL_WIDTH, width, EGL_HEIGHT, height, EGL_TEXTURE_OFFSET_X_ANGLE, offsetX, EGL_TEXTURE_OFFSET_Y_ANGLE, offsetY, EGL_NONE });
         }
     }
 }