[Xamarin.Android.Build.Tasks] remove pdb2mdb

Remove where we `ILRepack` `pdb2mdb.exe` into
`Xamarin.Android.Build.Tasks.dll` and the `<ConvertDebuggingFiles/>`
MSBuild task. These are not used in .NET 6+, and can be removed in
xamarin-android/main.

In future PRs, I think we can remove:

* `ILRepack` completely
* `Xamarin.Android.Legacy.targets`
* Other unused MSBuild tasks

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Build.Tasks.csproj

@@ -23,9 +23,6 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <Reference Include="pdb2mdb.exe">
-      <HintPath>$(MicrosoftAndroidSdkOutDir)pdb2mdb.exe</HintPath>
-    </Reference>
     <Reference Include="Mono.CompilerServices.SymbolWriter.dll">
       <HintPath>$(MicrosoftAndroidSdkOutDir)Mono.CompilerServices.SymbolWriter.dll</HintPath>
     </Reference>

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Build.Tasks.targets

@@ -287,7 +287,6 @@
     <InputAssemblies Include="$(OutputPath)NuGet.Versioning.dll" />
     <InputAssemblies Include="$(OutputPath)System.Collections.Immutable.dll" />
     <InputAssemblies Include="$(OutputPath)System.Reflection.Metadata.dll" />
-    <InputAssemblies Include="$(OutputPath)pdb2mdb.exe" />
   </ItemGroup>
 
   <Target Name="ILRepacker"

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

@@ -356,7 +356,6 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
 		.pdb;
 		.xml;
 		.dll.config;
-		.dll.mdb;
 	</AllowedReferenceRelatedFileExtensions>
 </PropertyGroup>
 
@@ -405,15 +404,6 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
   />
 </Target>
 
-<!-- When looking for related files to copy, look for Mono debugging files as well -->
-<PropertyGroup>
-	<AllowedReferenceRelatedFileExtensions>
-		$(AllowedReferenceRelatedFileExtensions);
-		.dll.mdb;
-		.exe.mdb
-	</AllowedReferenceRelatedFileExtensions>
-</PropertyGroup>
-
 <ItemGroup>
 	<AndroidCustomMetaDataForReferences Include="@(_AndroidAssemblySkipCases)" />
 </ItemGroup>

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Legacy.targets

@@ -219,7 +219,6 @@ projects. .NET 5 projects will not import this file.
   </PropertyGroup>
 
   <UsingTask TaskName="Xamarin.Android.Tasks.CheckGoogleSdkRequirements"          AssemblyFile="Xamarin.Android.Build.Tasks.dll" />
-  <UsingTask TaskName="Xamarin.Android.Tasks.ConvertDebuggingFiles"               AssemblyFile="Xamarin.Android.Build.Tasks.dll" />
   <UsingTask TaskName="Xamarin.Android.Tasks.CreateLibraryResourceArchive"        AssemblyFile="Xamarin.Android.Build.Tasks.dll" />
   <UsingTask TaskName="Xamarin.Android.Tasks.CreateManagedLibraryResourceArchive" AssemblyFile="Xamarin.Android.Build.Tasks.dll" />
   <UsingTask TaskName="Xamarin.Android.Tasks.CreateNativeLibraryArchive"          AssemblyFile="Xamarin.Android.Build.Tasks.dll" />
@@ -388,17 +387,10 @@ projects. .NET 5 projects will not import this file.
       <Output TaskParameter="PdbFiles" ItemName="_ResolvedPdbFiles" />
       <Output TaskParameter="PortablePdbFiles" ItemName="_ResolvedPortablePdbFiles" />
     </CollectPdbFiles>
-    <ItemGroup>
-      <_ConvertedMdbFiles Include="@(_ResolvedPdbFiles->'%(RootDir)%(Directory)%(Filename).dll.mdb')" />
-    </ItemGroup>
   </Target>
 
   <Target Name="_ConvertPdbFiles"
-      Inputs="@(_ResolvedPdbFiles)"
-      Outputs="@(_ConvertedMdbFiles)"
       DependsOnTargets="_CollectPdbFiles">
-    <ConvertDebuggingFiles Files="@(_ResolvedPdbFiles)" />
-    <Touch Files="@(_ConvertedMdbFiles)" ContinueOnError="true" />
     <ItemGroup>
       <!-- NOTE: @(_ResolvedPortablePdbFiles) are valid -->
       <_DeprecatedSymbols Include="@(_ResolvedMdbFiles);@(_ResolvedPdbFiles)" />
@@ -408,26 +400,9 @@ projects. .NET 5 projects will not import this file.
         FormatArguments="%(_DeprecatedSymbols.FileName)%(_DeprecatedSymbols.Extension)"
         Condition=" '%(_DeprecatedSymbols.Identity)' != '' "
     />
-    <ItemGroup>
-      <FileWrites Include="@(_ConvertedMdbFiles)" />
-    </ItemGroup>
   </Target>
 
-  <Target Name="ConvertDebuggingFiles"
-      Condition=" '$(AndroidIncludeDebugSymbols)' == 'true' And Exists ('$(_IntermediatePdbFile)') And '$(OS)' == 'Windows_NT'"
-      DependsOnTargets="_ConvertDebuggingFiles"
-  />
-
-  <Target Name="_ConvertDebuggingFiles"
-      Inputs="$(OutDir)$(TargetFileName);$(_IntermediatePdbFile)"
-      Outputs="$(OutDir)$(TargetFileName).mdb"
-      DependsOnTargets="_ValidateAndroidPackageProperties">
-    <ConvertDebuggingFiles Files="$(OutDir)$(TargetFileName)" />
-    <Touch Files="$(OutDir)$(TargetFileName).mdb" />
-    <ItemGroup>
-      <FileWrites Include="$(OutDir)$(TargetFileName).mdb" />
-    </ItemGroup>
-  </Target>
+  <Target Name="ConvertDebuggingFiles" />
 
   <Target Name="_AddAndroidEnvironmentToCompile">
     <ItemGroup>