Adjust module autoloads.

In Guile < 2.9.7, autoloading a module would give you access to all its
bindings.  In future versions, autoloading a module gives access only to
the listed bindings, as per #:select (see <https://bugs.gnu.org/38895>).

This commit adjusts autoloads to the new semantics, allowing Guix to be
built with Guile 2.9.7/2.9.8.

* guix/build/download.scm <top level>: Remove call to 'module-autoload!'.
(load-gnutls): New procedure.
(tls-wrap): Call it.
* guix/git.scm <top level>: Remove call to 'module-autoload!'.
(load-git-submodules): New procedure.
(update-submodules): Call it instead of 'resolve-interface'.
* gnu/bootloader/grub.scm: Replace #:autoload with #:use-module.
* gnu/packages.scm: Likewise.
* gnu/packages/ssh.scm: Likewise.
* gnu/packages/tex.scm: Likewise.
* gnu/services/cuirass.scm: Likewise.
* gnu/services/mcron.scm: Likewise.
* guix/lint.scm: Augment list of bindings in #:autoload.
* guix/scripts/build.scm: Likewise.
* guix/scripts/gc.scm: Likewise.
* guix/scripts/pack.scm: Likewise.
* guix/scripts/publish.scm: Likewise.
* guix/scripts/pull.scm: Likewise.
* guix/utils.scm: Remove unnecessary #:autoload clauses; replace one
of them with #:use-module.