Remove unused legacy PB_ properties (#15265)

Author: mmitche

src/SourceBuild/content/repo-projects/Directory.Build.props

@@ -68,7 +68,6 @@
 
     <EnvironmentVariables Include="PreReleaseVersionLabel=$(PreReleaseVersionLabel)" />
     <EnvironmentVariables Include="PackageVersionStamp=$(PreReleaseVersionLabel)" />
-    <EnvironmentVariables Include="PB_VersionStamp=$(PreReleaseVersionLabel)" />
 
     <!-- We pass '-ci', but also apply ci mode via env var for edge cases. (E.g. misbehaving inner builds.) -->
     <EnvironmentVariables Include="ContinuousIntegrationBuild=true" />

src/SourceBuild/content/repo-projects/sdk.proj

@@ -10,9 +10,6 @@
     <LogVerbosityOptOut>true</LogVerbosityOptOut>
     <BuildCommandArgs>$(BuildCommandArgs) -v $(LogVerbosity)</BuildCommandArgs>
 
-    <!-- Pass in package version props using the Product Construction (ProdCon) API. -->
-    <BuildCommandArgs>$(BuildCommandArgs) /p:PB_PackageVersionPropsUrl=file:%2F%2F$(PackageVersionPropsPath)</BuildCommandArgs>
-
     <BuildCommand>$(StandardSourceBuildCommand) $(BuildCommandArgs)</BuildCommand>
 
     <!-- NuGet SDK resolver only checks nuget.config files. https://github.com/Microsoft/msbuild/issues/2914 -->