Revert "module: fix check for package.json at volume root"

This reverts commit 51af89f.

This has needed to be backed out of both the 14.5.0 and 14.6.0
releases due to creating regressions across multiple projects
including:

* coffeescript
* JSONStream
* gulp
* and more

We should reopen a PR to figure out how to land this in a way
that is non-breaking.

Refs: nodejs#33476

Author: MylesBorins

lib/internal/modules/cjs/loader.js

@@ -49,7 +49,6 @@ const {
   SafeSet,
   String,
   StringPrototypeIndexOf,
-  StringPrototypeLastIndexOf,
   StringPrototypeMatch,
   StringPrototypeSlice,
   StringPrototypeStartsWith,
@@ -310,13 +309,12 @@ function readPackageScope(checkPath) {
   const rootSeparatorIndex = checkPath.indexOf(path.sep);
   let separatorIndex;
   while (
-    (separatorIndex = StringPrototypeLastIndexOf(checkPath, path.sep)) >=
-     rootSeparatorIndex
+    (separatorIndex = checkPath.lastIndexOf(path.sep)) > rootSeparatorIndex
   ) {
     checkPath = checkPath.slice(0, separatorIndex);
     if (checkPath.endsWith(path.sep + 'node_modules'))
       return false;
-    const pjson = readPackage(checkPath + path.sep);
+    const pjson = readPackage(checkPath);
     if (pjson) return {
       path: checkPath,
       data: pjson