Remove util/reconf

Remove util/reconf

The bulk of the util/reconf script is to detect old versions of
autoconf and possibly work around bugs in them.  Require
autoconf>=2.63, and remove the util/reconf script.  Adjust
documentation and other scripts accordingly.

Also remove Makefile rules that remove autom4te.cache.  Such rules
were supposedly necessary when mixing of different versions of
autoconf was common; this seems to be less of an issue now.

ticket: 8299
subject: Remove util/reconf