404: message, avoid mentioning "package gone"
404: message, avoid mentioning "package gone"

as 404 is returned for several different kind of missing pages

sophiejjj/debsources,nonas/debian-qa,clemux/debsources,clemux/debsources,devoxel/debsources,nonas/debian-qa,devoxel/debsources,vivekanand1101/debsources,vivekanand1101/debsources,clemux/debsources,matthieucan/debsources,zacchiro/debsources,zacchiro/debsources,Debian/debsources,zacchiro/debsources,oorestisime/debsources,clemux/debsources,vivekanand1101/debsources,sophiejjj/debsources,oorestisime/debsources,matthieucan/debsources,matthieucan/debsources,matthieucan/debsources,clemux/debsources,devoxel/debsources,vivekanand1101/debsources,oorestisime/debsources,zacchiro/debsources,sophiejjj/debsources,oorestisime/debsources,oorestisime/debsources,Debian/debsources,nonas/debian-qa,devoxel/debsources,sophiejjj/debsources,matthieucan/debsources,vivekanand1101/debsources,zacchiro/debsources,sophiejjj/debsources,devoxel/debsources,Debian/debsources,Debian/debsources,Debian/debsources,nonas/debian-qa