go/build: cgoEnabled is not known to cmd/dist anymore

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5901051

src/pkg/go/build/build.go

@@ -210,7 +210,6 @@ func (ctxt *Context) SrcDirs() []string {
 // if set, or else the compiled code's GOARCH, GOOS, and GOROOT.
 var Default Context = defaultContext()
 
-// This list is also known to ../../../cmd/dist/build.c.
 var cgoEnabled = map[string]bool{
 	"darwin/386":    true,
 	"darwin/amd64":  true,