module: remove dead code

This removes a lot of code that has no functionality anymore. All
Node.js internal code calls `_resolveLookupPaths` with two arguments.

The code that validates `index.js` is not required at all as we check
for these files anyway, so it's just redundant code that should be
removed.

PR-URL: https://github.com/nodejs/node/pull/26983
Refs: https://github.com/nodejs/node/pull/25362


Reviewed-By: Jan Krems <jan.krems@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>