maint: revert to `-1` rockspec revisions number.

* configure.ac (AC_INIT): Bump version to 34.1.
* rockspecs.lua: Revert to `-1` rockspec revision number.
* mkrockspecs.lua (specfile): Likewise.
* GNUmakefile (tag-release, check-in-release): Don't apply -2
suffix.
(release): Use -1 revision rockspec filename.