Tidy up some Core shared source files (Azure#38447)

* Remove LLPH and update PH

* remove another unused file

* restore PageableHelpers

Author: annelo-msft

eng/Directory.Build.Common.targets

@@ -208,7 +208,6 @@
     <Compile Include="$(AzureCoreSharedSources)IUtf8JsonSerializable.cs" LinkBase="Shared/Core" />
     <Compile Include="$(AzureCoreSharedSources)IXmlSerializable.cs" LinkBase="Shared/Core" />
     <Compile Include="$(AzureCoreSharedSources)JsonElementExtensions.cs" LinkBase="Shared/Core" />
-    <Compile Include="$(AzureCoreSharedSources)LowLevelPageableHelpers.cs" LinkBase="Shared/Core" />
     <Compile Include="$(AzureCoreSharedSources)NextLinkOperationImplementation.cs" LinkBase="Shared/Core" />
     <Compile Include="$(AzureCoreSharedSources)OperationFinalStateVia.cs" LinkBase="Shared/Core" />
     <Compile Include="$(AzureCoreSharedSources)OperationHelpers.cs" LinkBase="Shared/Core" />

sdk/appconfiguration/Azure.Data.AppConfiguration/src/Azure.Data.AppConfiguration.csproj

@@ -22,7 +22,6 @@
     <Compile Include="$(AzureCoreSharedSources)AzureResourceProviderNamespaceAttribute.cs" LinkBase="Shared" />
     <Compile Include="$(AzureCoreSharedSources)ConnectionString.cs" LinkBase="Shared" />
     <Compile Include="$(AzureCoreSharedSources)ArrayBufferWriter.cs" LinkBase="Shared" />
-    <Compile Include="$(AzureCoreSharedSources)ConditionalRequestOptionsExtensions.cs" LinkBase="Shared" />
     <Compile Include="$(AzureCoreSharedSources)HashCodeBuilder.cs" LinkBase="Shared" />
     <Compile Include="$(AzureCoreSharedSources)NoBodyResponseOfT.cs" LinkBase="Shared" />
     <Compile Include="$(AzureCoreSharedSources)PageResponseEnumerator.cs" LinkBase="Shared" />

sdk/core/Azure.Core/src/Shared/ConditionalRequestOptionsExtensions.cs

@@ -49,7 +49,6 @@
     <Compile Include="..\src\Shared\IXmlSerializable.cs" LinkBase="Shared" />
     <Compile Include="..\src\Shared\JsonElementExtensions.cs" LinkBase="Shared" />
     <Compile Include="..\src\Shared\LightweightPkcs8Decoder.cs" LinkBase="Shared" />
-    <Compile Include="..\src\Shared\LowLevelPageableHelpers.cs" LinkBase="Shared" />
     <Compile Include="..\src\Shared\NextLinkOperationImplementation.cs" LinkBase="Shared" />
     <Compile Include="..\src\Shared\NoBodyResponseOfT.cs" LinkBase="Shared" />
     <Compile Include="..\src\Shared\NoValueResponseOfT.cs" LinkBase="Shared" />