doc: stop generating defines.texi from configure

* generating defines.texi from configure means quagga.info will always have
  to be rebuilt by end-users, even from dist tarballs. Also breaks
  distcheck assumptions that info won't need to be built - which can be
  fixed with 'info-in-builddir' automake option, but that's too recent
  to rely on.
* doc/defines.texi.in: nuke
* doc/defines.texi: Add static version.
* {doc/Makefile.am,configure}: nuke autogen of above
* doc/quagga.texi: remove the 1 use of PACKAGE_STRING
5 files changed