* guix/build/download.scm (open-connection-for-uri): Add note about
same-named binding in Guile 2.2.0.
* guix/http-client.scm: Use 'guix:open-connection-for-uri' for the
procedure coming from (guix build download).
* guix/scripts/lint.scm: Likewise.
* guix/scripts/substitute.scm: Likewise.