Drop -preview tag for 15.9 release (#3837)
Drop -preview tag for 15.9 release (#3837)


AndyGerlicher/msbuild,chipitsine/msbuild,rainersigwald/msbuild,Microsoft/msbuild,cdmihai/msbuild,jeffkl/msbuild,jeffkl/msbuild,jeffkl/msbuild,mono/msbuild,Microsoft/msbuild,mono/msbuild,AndyGerlicher/msbuild,mono/msbuild,rainersigwald/msbuild,Microsoft/msbuild,chipitsine/msbuild,chipitsine/msbuild,mono/msbuild,AndyGerlicher/msbuild,cdmihai/msbuild,sean-gilliam/msbuild,cdmihai/msbuild,sean-gilliam/msbuild,cdmihai/msbuild,AndyGerlicher/msbuild,Microsoft/msbuild,rainersigwald/msbuild,jeffkl/msbuild,sean-gilliam/msbuild,rainersigwald/msbuild,sean-gilliam/msbuild,chipitsine/msbuild