Restore messages of old login and signup forms

The change 44840d15929d8ecfc1d7c31d6f7e86d873ac15a2 "Only new vertical format login and signup forms" removed
some messages no longer used in core, but 'userlogin' is used by
extensions including MobileFrontend

This restores the messages but marks them as unused in core and deprecated.

Change-Id: I82c4fc37481a4a0dea1e839238188f6555e3c60d
Merge "Restore messages of old login and signup forms"