remove package js_util

[jezell]

Compiling with --wasm in Flutter results in the following error messages:

Error: JS interop library 'dart:js_util' can't be imported when compiling to Wasm. Try using 'dart:js_interop' or 'dart:js_interop_unsafe' instead.

Also needs

#37

[Garciconx]

I have the same issue