Remove unused PLM code (#7)

Remove LayoutAwarePage, SuspensionManager, and other suspend-resume handling code. SuspensionManager::SaveAsync and related methods weren't actually called anywhere. I didn't attempt to remove the serialize/deserialize code at the ViewModel layer, although much of that is likely not needed either.

We may decide we want to persist more state through a suspend-terminate-resume cycle (as the app might have done a long time ago). But if we decide we want that, we should not use a persistence mechanism that's closely coupled to frame navigation.

src/Calculator/Views/MainPage.xaml

@@ -1,20 +1,20 @@
-<common:LayoutAwarePage x:Class="CalculatorApp.MainPage"
-                        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
-                        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-                        xmlns:automation="using:CalculatorApp.Common.Automation"
-                        xmlns:common="using:CalculatorApp.Common"
-                        xmlns:controls="using:CalculatorApp.Controls"
-                        xmlns:converters="using:CalculatorApp.Converters"
-                        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
-                        xmlns:local="using:CalculatorApp"
-                        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
-                        xmlns:muxc="using:Microsoft.UI.Xaml.Controls"
-                        xmlns:vm="using:CalculatorApp.ViewModel"
-                        x:Name="pageRoot"
-                        Background="{ThemeResource AppChromeAcrylicHostBackdropMediumLowBrush}"
-                        Loaded="OnPageLoaded"
-                        Unloaded="OnPageUnLoaded"
-                        mc:Ignorable="d">
+<Page x:Class="CalculatorApp.MainPage"
+      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+      xmlns:automation="using:CalculatorApp.Common.Automation"
+      xmlns:common="using:CalculatorApp.Common"
+      xmlns:controls="using:CalculatorApp.Controls"
+      xmlns:converters="using:CalculatorApp.Converters"
+      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+      xmlns:local="using:CalculatorApp"
+      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+      xmlns:muxc="using:Microsoft.UI.Xaml.Controls"
+      xmlns:vm="using:CalculatorApp.ViewModel"
+      x:Name="pageRoot"
+      Background="{ThemeResource AppChromeAcrylicHostBackdropMediumLowBrush}"
+      Loaded="OnPageLoaded"
+      Unloaded="OnPageUnLoaded"
+      mc:Ignorable="d">
 
     <Page.Resources>
         <automation:NarratorNotifier x:Name="NarratorNotifier"/>
@@ -160,4 +160,4 @@
             </Grid>
         </muxc:NavigationView>
     </Grid>
-</common:LayoutAwarePage>
+</Page>