Remove function prototype extensions

packages/@ember/-internals/environment/lib/env.ts

@@ -1,4 +1,3 @@
-import { FUNCTION_PROTOTYPE_EXTENSIONS } from '@ember/deprecated-features';
 import { DEBUG } from '@glimmer/env';
 import global from './global';
 
@@ -220,16 +219,10 @@ export const ENV = {
   if (EXTEND_PROTOTYPES !== undefined) {
     if (typeof EXTEND_PROTOTYPES === 'object' && EXTEND_PROTOTYPES !== null) {
       ENV.EXTEND_PROTOTYPES.String = EXTEND_PROTOTYPES.String !== false;
-      if (FUNCTION_PROTOTYPE_EXTENSIONS) {
-        ENV.EXTEND_PROTOTYPES.Function = EXTEND_PROTOTYPES.Function !== false;
-      }
       ENV.EXTEND_PROTOTYPES.Array = EXTEND_PROTOTYPES.Array !== false;
     } else {
       let isEnabled = EXTEND_PROTOTYPES !== false;
       ENV.EXTEND_PROTOTYPES.String = isEnabled;
-      if (FUNCTION_PROTOTYPE_EXTENSIONS) {
-        ENV.EXTEND_PROTOTYPES.Function = isEnabled;
-      }
       ENV.EXTEND_PROTOTYPES.Array = isEnabled;
     }
   }
@@ -259,6 +252,6 @@ export const ENV = {
   }
 })(global.EmberENV);
 
-export function getENV() {
+export function getENV(): object {
   return ENV;
 }

packages/@ember/-internals/metal/tests/observer_test.js

@@ -1,4 +1,3 @@
-import { ENV } from '@ember/-internals/environment';
 import {
   changeProperties,
   addObserver,
@@ -15,7 +14,6 @@ import {
   set,
 } from '..';
 import { moduleFor, AbstractTestCase, runLoopSettled } from 'internal-test-helpers';
-import { FUNCTION_PROTOTYPE_EXTENSIONS } from '@ember/deprecated-features';
 import { destroy } from '@glimmer/destroyable';
 import { meta as metaFor } from '@ember/-internals/meta';
 
@@ -192,91 +190,6 @@ moduleFor(
       assert.equal(observerCount, 10, 'should continue to fire indefinitely');
     }
 
-    async ['@test observer added via Function.prototype extensions and brace expansion should fire when property changes'](
-      assert
-    ) {
-      if (!FUNCTION_PROTOTYPE_EXTENSIONS && ENV.EXTEND_PROTOTYPES.Function) {
-        obj = {};
-        let count = 0;
-
-        expectDeprecation(() => {
-          mixin(obj, {
-            observeFooAndBar: function () {
-              count++;
-            }.observes('{foo,bar}'),
-          });
-        }, /Function prototype extensions have been deprecated, please migrate from function\(\){}.observes\('foo'\) to observer\('foo', function\(\) {}\)/);
-
-        set(obj, 'foo', 'foo');
-        await runLoopSettled();
-
-        assert.equal(count, 1, 'observer specified via brace expansion invoked on property change');
-
-        set(obj, 'bar', 'bar');
-        await runLoopSettled();
-
-        assert.equal(count, 2, 'observer specified via brace expansion invoked on property change');
-
-        set(obj, 'baz', 'baz');
-        await runLoopSettled();
-
-        assert.equal(count, 2, 'observer not invoked on unspecified property');
-      } else {
-        assert.expect(0);
-      }
-    }
-
-    async ['@test observer specified via Function.prototype extensions via brace expansion should fire when dependent property changes'](
-      assert
-    ) {
-      if (!FUNCTION_PROTOTYPE_EXTENSIONS && ENV.EXTEND_PROTOTYPES.Function) {
-        obj = { baz: 'Initial' };
-        let count = 0;
-
-        defineProperty(
-          obj,
-          'foo',
-          computed('bar', function () {
-            return get(this, 'bar').toLowerCase();
-          })
-        );
-
-        defineProperty(
-          obj,
-          'bar',
-          computed('baz', function () {
-            return get(this, 'baz').toUpperCase();
-          })
-        );
-
-        expectDeprecation(() => {
-          mixin(obj, {
-            fooAndBarWatcher: function () {
-              count++;
-            }.observes('{foo,bar}'),
-          });
-        }, /Function prototype extensions have been deprecated, please migrate from function\(\){}.observes\('foo'\) to observer\('foo', function\(\) {}\)/);
-
-        get(obj, 'foo');
-        set(obj, 'baz', 'Baz');
-        await runLoopSettled();
-
-        // fire once for foo, once for bar
-        assert.equal(
-          count,
-          2,
-          'observer specified via brace expansion invoked on dependent property change'
-        );
-
-        set(obj, 'quux', 'Quux');
-        await runLoopSettled();
-
-        assert.equal(count, 2, 'observer not fired on unspecified property');
-      } else {
-        assert.expect(0);
-      }
-    }
-
     async ['@test observers watching multiple properties via brace expansion should fire when the properties change'](
       assert
     ) {

packages/@ember/-internals/runtime/index.js

@@ -30,5 +30,3 @@ export { default as PromiseProxyMixin } from './lib/mixins/promise_proxy';
 
 export { default as RSVP, onerrorDefault } from './lib/ext/rsvp'; // just for side effect of extending Ember.RSVP
 export { typeOf } from './lib/type-of';
-
-import './lib/ext/function'; // just for side effect of extending Function.prototype