fix(zone.js): remove global declaration (#37861)

Close #37531

Remove `global` declaration in `zone.ts` to avoid compile error when
upgrade to `@types/node` v12.12.68. Since the new type of global become
`NodeJS.global & typeof globalThis` and not compatible with `zone.ts` declaration.

PR Close #37861

packages/zone.js/lib/zone-global.d.ts

@@ -0,0 +1,13 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+// CommonJS / Node have global context exposed as "global" variable.
+// This code should run in a Browser, so we don't want to include the whole node.d.ts
+// typings for this compilation unit.
+// We'll just fake the global "global" var for now.
+declare var global: NodeJS.Global;

packages/zone.js/lib/zone.ts

@@ -675,12 +675,6 @@ type AmbientZone = Zone;
 /** @internal */
 type AmbientZoneDelegate = ZoneDelegate;
 
-// CommonJS / Node have global context exposed as "global" variable.
-// This code should run in a Browser, so we don't want to include the whole node.d.ts
-// typings for this compilation unit.
-// We'll just fake the global "global" var for now.
-declare var global: NodeJS.Global;
-
 const Zone: ZoneType = (function(global: any) {
   const performance: {mark(name: string): void; measure(name: string, label: string): void;} =
       global['performance'];