Removed IPlatformThreadingInterface mock since it's broken anyway

tests/Perspex.Controls.UnitTests/Primitives/PopupTests.cs

@@ -267,7 +267,6 @@ namespace Perspex.Controls.UnitTests.Primitives
             PerspexLocator.CurrentMutable
                 .Bind<ILayoutManager>().ToTransient<LayoutManager>()
                 .Bind<IGlobalStyles>().ToFunc(() => globalStyles.Object)
-                .Bind<IPlatformThreadingInterface>().ToConstant(new Mock<IPlatformThreadingInterface>().Object)
                 .Bind<IPopupImpl>().ToConstant(new Mock<IPopupImpl>().Object)
                 .Bind<IStyler>().ToTransient<Styler>();
 

tests/Perspex.Controls.UnitTests/TopLevelTests.cs

@@ -326,7 +326,6 @@ namespace Perspex.Controls.UnitTests
                 .Bind<IGlobalStyles>().ToConstant(globalStyles.Object)
                 .Bind<ILayoutManager>().ToConstant(layoutManager)
                 .Bind<IPlatformRenderInterface>().ToConstant(renderInterface)
-                .Bind<IPlatformThreadingInterface>().ToConstant(new Mock<IPlatformThreadingInterface>().Object)
                 .Bind<IRenderQueueManager>().ToConstant(renderManager)
                 .Bind<IStyler>().ToConstant(new Styler());
         }

tests/Perspex.Layout.UnitTests/FullLayoutTests.cs

@@ -147,7 +147,6 @@ namespace Perspex.Layout.UnitTests
                 .Bind<IGlobalStyles>().ToConstant(globalStyles.Object)
                 .Bind<ILayoutManager>().ToConstant(new LayoutManager())
                 .Bind<IPlatformRenderInterface>().ToConstant(renderInterface)
-                .Bind<IPlatformThreadingInterface>().ToConstant(new Mock<IPlatformThreadingInterface>().Object)
                 .Bind<IRenderQueueManager>().ToConstant(renderManager)
                 .Bind<IStyler>().ToConstant(new Styler())
                 .Bind<IWindowImpl>().ToConstant(windowImpl.Object);