Remove `ember-cli-string-helpers` addon

[barryofguilder]

When I upgrade my addon to use @ember/string v4.0, my addon build will throw an error that says:

"Module not found: Error: ember-cli-string-helpers is trying to import the app's @ember/string package, but it seems to be missing"

I noticed that the ember-cli-string-helpers addon was archived in October 2024. I think it would be a good idea to remove this package and replace it with something that is maintained. For now, the way to fix this issue is by locking the version of @ember/string to 3.1.1.

[MichalBryxi]

For random bypassers:

fix this issue is by locking the version of @ember/string to 3.1.1.

Means:

// package.json
{
  "dependencies": {
    "@ember/string": "^3.1.1",
  },
}