Deprecate Ember.STRINGS

- Remove `getString` from string_registry, it was unused internally and
  not exposed publicly.

(cherry picked from commit e6a9f62)

Author: kategengler

packages/@ember/string/lib/string_registry.ts

@@ -1,16 +1,28 @@
+import { deprecate } from '@ember/debug';
+
 // STATE within a module is frowned upon, this exists
 // to support Ember.STRINGS but shield ember internals from this legacy global
 // API.
 let STRINGS: { [key: string]: string } = {};
 
 export function setStrings(strings: { [key: string]: string }) {
+  deprecateEmberStrings();
   STRINGS = strings;
 }
 
 export function getStrings(): { [key: string]: string } {
+  deprecateEmberStrings();
   return STRINGS;
 }
 
-export function getString(name: string): string | undefined {
-  return STRINGS[name];
+function deprecateEmberStrings() {
+  deprecate('Ember.STRINGS is deprecated. It is no longer used by Ember.', false, {
+    id: 'ember-strings',
+    for: 'ember-source',
+    since: {
+      available: '4.10',
+      enabled: '4.10.',
+    },
+    until: '5.0.0',
+  });
 }

packages/ember/tests/reexports_test.js

@@ -67,6 +67,16 @@ moduleFor(
       });
     }
 
+    ['@test Ember.STRINGS is deprecated'](assert) {
+      expectDeprecation(() => {
+        assert.ok(Ember.STRINGS);
+      }, 'Ember.STRINGS is deprecated. It is no longer used by Ember.');
+
+      expectDeprecation(() => {
+        Ember.STRINGS = {};
+      }, 'Ember.STRINGS is deprecated. It is no longer used by Ember.');
+    }
+
     '@test Ember.FEATURES is exported'(assert) {
       for (let feature in FEATURES) {
         assert.equal(