Remove redundant MSBuildBinPath import

MSBuildBinPath was replaced with MSBuildToolsPath after VS2005.
MSBuildBinPath was kept around for back-compat, but is no longer
needed. The extra import causes unnecessary build warnings.

See http://msdn.microsoft.com/en-us/library/bb397428.aspx for
a full discussion.
Merge pull request #388 from Haacked/remove-unneeded-import

Remove redundant MSBuildBinPath import