https://gerrit.wikimedia.org/r/#/c/67233/ remotes the old-style login and create account forms from core. The new forms have different messages, e.g. no more colons in English labels and there's no more use of the  combined "Log in / create account".  So I removed the old messages from MessagesEn.php, MessagesQqq.php and messages.inc.

Raimond Spekking pointed out

 'userlogin' message is still used by the OpenID extension.

Maybe more of these very old messages are used by other extensions.Needs investigation, partly revert recommended in the meantime.

Good point, 'userlogin' is also used by MobileFrontEnd and some unmaintained signup extensions.  I will prepare a patch that restores it.

I searched for message keys in single quotes and it seems the other messages I removed (yourname yourpasswordagain userlogin userloginnocreate nologin nologinlink gotaccount gotaccountlink userlogin-resetlink createaccountreason ) are unused by the the extensions in 1.22wmf7.

* Should I restore those other messages as well?

* Is there a process for deprecated or obsoleting a message in core?
* Should I put something in MessagesQqq.php saying "Unused in core but some extensions still use it"

FWIW mediawiki.org's I18n page and Manual:System_message#