DEV: delete nameValidation mixin (#31275)

This mixin is now ready for deletion, all uses of it has been removed
from plugins.

app/assets/javascripts/discourse/app/mixins/name-validation.js

@@ -1,43 +0,0 @@
-import EmberObject, { computed } from "@ember/object";
-import Mixin from "@ember/object/mixin";
-import { isEmpty } from "@ember/utils";
-import deprecated from "discourse/lib/deprecated";
-import { i18n } from "discourse-i18n";
-
-export default Mixin.create({
-  init() {
-    this._super(...arguments);
-
-    deprecated(
-      "NameValidation mixin is deprecated. Use the helper class from discourse/lib/name-validation-helper instead.",
-      {
-        id: "discourse.name-validation-mixin",
-        since: "v3.4.0.beta4-dev",
-      }
-    );
-  },
-
-  get nameTitle() {
-    return i18n(
-      this.site.full_name_required_for_signup
-        ? "user.name.title"
-        : "user.name.title_optional"
-    );
-  },
-
-  // Validate the name.
-  nameValidation: computed("accountName", "forceValidationReason", function () {
-    const { accountName, forceValidationReason } = this;
-    if (this.site.full_name_required_for_signup && isEmpty(accountName)) {
-      return EmberObject.create({
-        failed: true,
-        ok: false,
-        message: i18n("user.name.required"),
-        reason: forceValidationReason ? i18n("user.name.required") : null,
-        element: document.querySelector("#new-account-name"),
-      });
-    }
-
-    return EmberObject.create({ ok: true });
-  }),
-});