fix warnings, and bogosity in projectfiles

OpenRA.Renderer.Null/OpenRA.Renderer.Null.csproj

@@ -60,7 +60,6 @@
       <Name>OpenRA.Game</Name>
     </ProjectReference>
   </ItemGroup>
-  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.
@@ -69,4 +68,4 @@
   <Target Name="AfterBuild">
   </Target>
   -->
-</Project>
+</Project>