Use "guile-zlib" and "guile-lzlib" instead of (guix config).

* Makefile.am (MODULES): Remove guix/zlib.scm and guix/lzlib.scm,
(SCM_TESTS): remove tests/zlib.scm, tests/lzlib.scm.
* build-aux/build-self.scm (make-config.scm): Remove unused %libz variable.
* configure.ac: Remove LIBZ and LIBLZ variables and check instead for
Guile-zlib and Guile-lzlib.
* doc/guix.texi ("Requirements"): Remove zlib requirement and add Guile-zlib
and Guile-lzlib instead.
* gnu/packages/package-management.scm (guix)[native-inputs]: Add "guile-zlib"
and "guile-lzlib",
[inputs]: remove "zlib" and "lzlib",
[propagated-inputs]: ditto,
[arguments]: add "guile-zlib" and "guile-lzlib" to Guile load path.
* guix/config.scm.in (%libz, %liblz): Remove them.
* guix/lzlib.scm: Remove it.
* guix/man-db.scm: Use (zlib) instead of (guix zlib).
* guix/profiles.scm (manual-database): Do not stub (guix config) in imported
modules list, instead add "guile-zlib" to the extension list.
* guix/scripts/publish.scm: Use (zlib) instead of (guix zlib) and (lzlib)
instead of (guix lzlib),
(string->compression-type, effective-compression): do not check for zlib and
lzlib availability.
* guix/scripts/substitute.scm (%compression-methods): Do not check for lzlib
availability.
* guix/self.scm (specification->package): Add "guile-zlib" and "guile-lzlib"
and remove "zlib" and "lzlib",
(compiled-guix): remove "zlib" and "lzlib" arguments and add guile-zlib and
guile-lzlib to the dependencies, also do not pass "zlib" and "lzlib" to
"make-config.scm" procedure,
(make-config.scm): remove "zlib" and "lzlib" arguments as well as %libz and
%liblz variables.
* guix/utils.scm (lzip-port): Use (lzlib) instead of (guix lzlib) and do not
check for lzlib availability.
* guix/zlib.scm: Remove it.
* m4/guix.m4 (GUIX_LIBZ_LIBDIR, GUIX_LIBLZ_FILE_NAME): Remove them.
* tests/lzlib.scm: Use (zlib) instead of (guix zlib) and (lzlib)
instead of (guix lzlib), and do not check for zlib and lzlib availability.
* tests/publish.scm: Ditto.
* tests/substitute.scm: Do not check for lzlib availability.
* tests/utils.scm: Ditto.
* tests/zlib.scm: Remove it.