module: mark DEP0019 as EOL and remove compat code

This removes the compatibilty code that was in place to allow an unintended
interaction between `require('.')` and `NODE_PATH`. The compatibility code and
the accompanying deprecation warning has been in place since 2015-04-17.

PR-URL: https://github.com/nodejs/node/pull/3384


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>