Switch to Guile-Gcrypt.

This removes (guix hash) and (guix pk-crypto), which now live as part of
Guile-Gcrypt (version 0.1.0.)

* guix/gcrypt.scm, guix/hash.scm, guix/pk-crypto.scm,
tests/hash.scm, tests/pk-crypto.scm: Remove.
* configure.ac: Test for Guile-Gcrypt.  Remove LIBGCRYPT and
LIBGCRYPT_LIBDIR assignments.
* m4/guix.m4 (GUIX_ASSERT_LIBGCRYPT_USABLE): Remove.
* README: Add Guile-Gcrypt to the dependencies; move libgcrypt as
"required unless --disable-daemon".
* doc/guix.texi (Requirements): Likewise.
* gnu/packages/bash.scm, guix/derivations.scm, guix/docker.scm,
guix/git.scm, guix/http-client.scm, guix/import/cpan.scm,
guix/import/cran.scm, guix/import/crate.scm, guix/import/elpa.scm,
guix/import/gnu.scm, guix/import/hackage.scm,
guix/import/texlive.scm, guix/import/utils.scm, guix/nar.scm,
guix/pki.scm, guix/scripts/archive.scm,
guix/scripts/authenticate.scm, guix/scripts/download.scm,
guix/scripts/hash.scm, guix/scripts/pack.scm,
guix/scripts/publish.scm, guix/scripts/refresh.scm,
guix/scripts/substitute.scm, guix/store.scm,
guix/store/deduplication.scm, guix/tests.scm, tests/base32.scm,
tests/builders.scm, tests/challenge.scm, tests/cpan.scm,
tests/crate.scm, tests/derivations.scm, tests/gem.scm,
tests/nar.scm, tests/opam.scm, tests/pki.scm,
tests/publish.scm, tests/pypi.scm, tests/store-deduplication.scm,
tests/store.scm, tests/substitute.scm: Adjust imports.
* gnu/system/vm.scm: Likewise.
(guile-sqlite3&co): Rename to...
(gcrypt-sqlite3&co): ... this.  Add GUILE-GCRYPT.
(expression->derivation-in-linux-vm)[config]: Remove.
(iso9660-image)[config]: Remove.
(qemu-image)[config]: Remove.
(system-docker-image)[config]: Remove.
* guix/scripts/pack.scm: Adjust imports.
(guile-sqlite3&co): Rename to...
(gcrypt-sqlite3&co): ... this.  Add GUILE-GCRYPT.
(self-contained-tarball)[build]: Call 'make-config.scm' without
 #:libgcrypt argument.
(squashfs-image)[libgcrypt]: Remove.
[build]: Call 'make-config.scm' without #:libgcrypt.
(docker-image)[config, json]: Remove.
[build]: Add GUILE-GCRYPT to the extensions  Remove (guix config) from
the imported modules.
* guix/self.scm (specification->package): Remove "libgcrypt", add
"guile-gcrypt".
(compiled-guix): Remove #:libgcrypt.
[guile-gcrypt]: New variable.
[dependencies]: Add it.
[*core-modules*]: Remove #:libgcrypt from 'make-config.scm' call.
Add #:extensions.
[*config*]: Remove #:libgcrypt from 'make-config.scm' call.
(%dependency-variables): Remove %libgcrypt.
(make-config.scm): Remove #:libgcrypt.
* build-aux/build-self.scm (guile-gcrypt): New variable.
(make-config.scm): Remove #:libgcrypt.
(build-program)[fake-gcrypt-hash]: New variable.
Add (gcrypt hash) to the imported modules.  Adjust load path
assignments.
* gnu/packages/package-management.scm (guix)[propagated-inputs]: Add
GUILE-GCRYPT.
[arguments]: In 'wrap-program' phase, add GUILE-GCRYPT to the search
path.

README

@@ -21,7 +21,7 @@ Guix is based on the [[https://nixos.org/nix/][Nix]] package manager.
 GNU Guix currently depends on the following packages:
 
   - [[https://gnu.org/software/guile/][GNU Guile 2.2.x or 2.0.x]], version 2.0.13 or later
-  - [[https://gnupg.org/][GNU libgcrypt]]
+  - [[https://notabug.org/cwebber/guile-gcrypt][Guile-Gcrypt]] 0.1.0 or later
   - [[https://www.gnu.org/software/make/][GNU Make]]
   - [[https://www.gnutls.org][GnuTLS]] compiled with guile support enabled
   - [[https://notabug.org/civodul/guile-sqlite3][Guile-SQLite3]], version 0.1.0 or later
@@ -31,6 +31,7 @@ GNU Guix currently depends on the following packages:
 
 Unless `--disable-daemon' was passed, the following packages are needed:
 
+  - [[https://gnupg.org/][GNU libgcrypt]]
   - [[https://sqlite.org/][SQLite 3]]
   - [[https://gcc.gnu.org][GCC's g++]]
   - optionally [[http://www.bzip.org][libbz2]]