common: remove dead code

The referenced bug was fixed in Go 1.2,
and Packer requires Go 1.2+.

common/config.go

@@ -161,14 +161,6 @@ func DownloadableURL(original string) (string, error) {
 	// Make sure it is lowercased
 	url.Scheme = strings.ToLower(url.Scheme)
 
-	// This is to work around issue #5927. This can safely be removed once
-	// we distribute with a version of Go that fixes that bug.
-	//
-	// See: https://code.google.com/p/go/issues/detail?id=5927
-	if url.Path != "" && url.Path[0] != '/' {
-		url.Path = "/" + url.Path
-	}
-
 	// Verify that the scheme is something we support in our common downloader.
 	supported := []string{"file", "http", "https"}
 	found := false