msbuild: use default Project attrs

maybe it makes the xml less scary :D

Externals/cpp-optparse/cpp-optparse.vcxproj

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<Project>
   <Import Project="..\..\Source\VSProps\Base.Macros.props" />
   <Import Project="$(VSPropsDir)Base.Targets.props" />
   <PropertyGroup Label="Globals">