AJSDCE acorn pass can strip "use strict";

[sbc100]

It turns "use strict"; into null;.

This on its own is maybe not that bad, but that ends up generating a closure warning:

a.out.jso4.js:1:0: WARNING - [JSC_USELESS_CODE] Suspicious code. This code lacks side-effects. Is there a bug?
  1| null;
     ^^^^

This is the root cause of #17939