The next commits make (sqlite3) an indirect dependency of (gnu build
install), which is itself used by (guix scripts system), hence this new
requirement.

* configure.ac: Error out when $guix_cv_have_recent_guile_sqlite3 is
false.  Remove HAVE_GUILE_SQLITE3 Automake conditional.
* Makefile.am (MODULES, SCM_TESTS): Remove HAVE_GUILE_SQLITE3 conditions.
* doc/guix.texi (Requirements): Add Guile-SQLite3.
* README: Ditto.
* gnu/packages/package-management.scm (guix)[propagated-inputs]: Add
GUILE-SQLITE3.
[arguments]: In 'wrap-program' phase, take guile-sqlite3 into account.