Remove total confusion from git-fetch and git-push

Remove total confusion from git-fetch and git-push

The config file is not the only place remotes are defined, and without
consulting .git/remotes and .git/branches, you won't know if "origin" is
configured by the user.  Don't give up too early and insult the user with
a wisecrack "Where do you want to fetch from today?"

The only thing the previous patch seems to want to prevent from happening
is a lazy "git fetch/push" that does not say where-from/to to produce an
error message 'origin not found', and we can do that by not letting
add_url_alias() to turn a nickname "origin" literally into a pathname
"origin" without changing the rest of the logic.

Signed-off-by: Junio C Hamano <gitster@pobox.com>