moduleLoad spuriously fires on ES6 imports

[robfig]

When using rules_closure to compile a trivial js application that uses ES6 modules, compilation fails unless moduleLoad is suppressed.

This can be seen in #409

[gkdn]

@alexeagle b/129555304 is the internal underlying bug tracking this.

[alexeagle]

Seems like this is a bug in https://github.com/google/closure-compiler, not rules_closure right? In the sense that it can be reproduced in the former.

My hope is to remove all Java code from this repo so there is no surface for bugs that aren't reproducible in the compiler itself.