Remove readline notice from psql --version?

Currently, psql --version prints something like

psql (PostgreSQL) 9.2beta1
contains support for command-line editing

I think the notice about readline is a leftover from the old days when
psql was often built without any readline support.  Nowadays, this looks
like an anomaly, and it doesn't actually contain any information that
would be useful nowadays, such as which particular library is used or
what kind of history support is active.  I suggest we remove this second
line, or alternatively, we could add more useful detail, but what?