Among other things, this removes (guix utils), (guix ui), (guix config),
etc. from the closure of (guix build download), as was the case since
798648515b.
* guix/utils.scm (<progress-reporter>, call-with-progress-reporter):
Move to...
* guix/progress.scm: ... here. New file.
* Makefile.am (MODULES): Add it.
* guix/build/download.scm (current-terminal-columns)
(nearest-exact-integer, duration->seconds, seconds->string)
(byte-count->string, progress-bar, string-pad-middle)
(rate-limited, progress-reporter/file, dump-port*)
(time-monotonic): Move to progress.scm.
* guix/scripts/download.scm: Adjust accordingly.
* guix/scripts/substitute.scm: Likewise.
8c3488259e