ffi: simplify Symbol.dispose assignment

Use a direct prototype assignment for DynamicLibrary.prototype[Symbol.dispose],
matching the style used elsewhere in the codebase (e.g. Timers).

Author: mcollina

lib/ffi.js

@@ -1,7 +1,6 @@
 'use strict';
 
 const {
-  ObjectDefineProperty,
   ObjectFreeze,
   ObjectPrototypeToString,
   SymbolDispose,
@@ -55,14 +54,9 @@ const {
   toArrayBuffer,
 } = internalBinding('ffi');
 
-ObjectDefineProperty(DynamicLibrary.prototype, SymbolDispose, {
-  __proto__: null,
-  configurable: true,
-  writable: true,
-  value: function dispose() {
-    this.close();
-  },
-});
+DynamicLibrary.prototype[SymbolDispose] = function() {
+  this.close();
+};
 
 function checkFFIPermission() {
   if (!permission.isEnabled() || permission.has('ffi')) {