Drop support for legacy `hub.http-clone` git config value

This was kept for backwards compatibility, but was silently broken for
some tiem now. Nobody reported it, so I think it can be safely assumes
that nobody uses this config value anymore.

github/util.go

@@ -10,10 +10,5 @@ func IsHttpsProtocol() bool {
 		return true
 	}
 
-	httpClone, _ := git.Config("--bool hub.http-clone")
-	if httpClone == "true" {
-		return true
-	}
-
 	return false
 }