Change QUrlPrivate::setAuthority to return void

Change QUrlPrivate::setAuthority to return void

It used to return bool because setHost returns bool and, therefore,
setAuthority could fail. However, the return value is never checked,
in either parse() or QUrl::setAuthority(), because there's no error
recovery.

This is a small optimisation.

Change-Id: I25660d66cfad64ca5b9706cc38afa0e97ba3ee0b
Reviewed-by: Shane Kearns <shane.kearns@accenture.com>
Reviewed-by: David Faure <faure@kde.org>