fix: std/portable included twice

[JairusSW]

Whenever importing from within a transform,

import { Transform } from "assemblyscript/dist/transform.js";
import { Parser } from "assemblyscript/dist/assemblyscript.js";

I get the following warning:

compiler mismatch: std/portable included twice

The warning occurs with nearly every transform I have written and since it writes to stderr which is problematic.

Instead of warning the user when std/portable is imported twice, it seems more reasonable just to ignore it altogether. After all, its the compiler importing it twice, not the user.