Remove (guix http) and (guix ftp).

Remove (guix http) and (guix ftp).

* guix/ftp.scm, guix/http.scm, guix/build/ftp.scm, guix/build/http.scm:
  Remove.
* Makefile.am (MODULES): Likewise.
* tests/builders.scm, distro/packages/base.scm,
  distro/packages/bash.scm, distro/packages/bdw-gc.scm,
  distro/packages/compression.scm, distro/packages/gawk.scm,
  distro/packages/gnupg.scm, distro/packages/gperf.scm,
  distro/packages/guile.scm, distro/packages/libffi.scm,
  distro/packages/libsigsegv.scm, distro/packages/libtool.scm,
  distro/packages/libunistring.scm, distro/packages/lout.scm,
  distro/packages/m4.scm, distro/packages/multiprecision.scm,
  distro/packages/ncurses.scm, distro/packages/perl.scm,
  distro/packages/pkg-config.scm, distro/packages/pth.scm,
  distro/packages/readline.scm, distro/packages/recutils.scm: Use
  `url-fetch' instead of `http-fetch' and `ftp-fetch'.
* distro/packages/bootstrap.scm: Likewise
  (bootstrap-origin): Remove references to `http-fetch' and
  `ftp-fetch'.
* guix.scm (%public-modules): Remove `http' and `ftp'; add `download'.