gitweb: Do not automatically append " git" to custom site name

gitweb: Do not automatically append " git" to custom site name

If you customized the site name, you probably do not want the " git"
appended so that the page title is not bastardized; I want repo.or.cz pages
titled "Public Git Hosting", not "Public Git Hosting git" (what's hosting
what?).

This slightly changes the $site_name semantics but only very
insignificantly.

Signed-off-by: Petr Baudis <pasky@suse.cz>
Signed-off-by: Junio C Hamano <junkio@cox.net>