Update docbook_3 to version 3.1 / rev 22 via SR 1088783
https://build.opensuse.org/request/show/1088783
by user pluskalm + dimstar_suse
- Modernise spec file a bit
- Rename docbook_3-README.SuSE to docbook_3-README.SUSE
- remove several other URLs (which are no longer available at
the old address or elsewhere)
- fix URL of dbhset.tar.gz (no longer available at the old HTTP
address or elsewhere).