Make esmock slightly smaller

[iambumblehead]

These changes are made for fun while waiting for someone to call me today. Basically, this PR should make esmock slightly smaller and more readable.

A recursive function is renamed and an unused param was removed. And many other little micro-optimizations...

-const esmockModulesCreate = async (parent, moduleFileURL, esmockKey, defs, keys, mocks, opt) => {
+const esmockModuleId = async (parent, key, defs, ids, mocks, opt) => {
  // ...
  if (keys.length)
-   return esmockModulesCreate(parent, moduleFileURL, esmockKey, defs, keys.slice(1), mocks, opt)
+   return esmockModuleId(parent, key, defs, ids.slice(1), mocks, opt)
}

[tripodsan]

LGTM, judging by the diff