Removed a bad reference from VsixUtil

The VsixUtil project incorrectly had an explicit reference to the
extension manager package and the VisualStudio namespace.  This was from
an earlier iteration of the code base that wasn't as dynamic.  It was
preventing a build on machines that didn't have Visual Studio 2010
installed.  Remove the unnecessary code
Merge branch 'master' of https://github.com/jaredpar/VsVim