refactor: don't expose isPromise as an internal module (#19139)

lib/common/api/module-list.js

@@ -6,6 +6,5 @@ module.exports = [
   { name: 'nativeImage', loader: () => require('./native-image') },
   { name: 'shell', loader: () => require('./shell') },
   // The internal modules, invisible unless you know their names.
-  { name: 'deprecate', loader: () => require('./deprecate'), private: true },
-  { name: 'isPromise', loader: () => require('./is-promise'), private: true }
+  { name: 'deprecate', loader: () => require('./deprecate'), private: true }
 ]

lib/common/is-promise.ts

@@ -1,6 +1,4 @@
-'use strict'
-
-module.exports = function isPromise (val) {
+export function isPromise (val: any) {
   return (
     val &&
     val.then &&