Revert "React to deprecation of Fedora.28.Amd64.Open"

This reverts 83eeeec10c6eb68b423855078ff1c0b529d0fad6

eng/targets/Helix.Common.props

@@ -23,7 +23,7 @@
     <HelixAvailableTargetQueue Include="Debian.8.Amd64.Open" Platform="Linux" />
     <HelixAvailableTargetQueue Include="Debian.9.Amd64.Open" Platform="Linux" />
     <HelixAvailableTargetQueue Include="Redhat.7.Amd64.Open" Platform="Linux" />
-    <HelixAvailableTargetQueue Include="(Fedora.28.Amd64.Open)[email protected]/dotnet-buildtools/prereqs:fedora-28-helix-09ca40b-20190508143249" Platform="Linux" />
+    <HelixAvailableTargetQueue Include="Fedora.28.Amd64.Open" Platform="Linux" />
 
     <!--  TODO: re-enable Debian.9.Arm64.Open and Ubuntu.1804.Arm64.Open    -->
   </ItemGroup>