guix: Strip #:use-module lists.

This was obtained by setting up this environment:

  guix shell -D guix --with-input=guile@3.0.9=guile-next \
    --with-commit=guile-next=e2ed33ef0445c867fe56c247054aa67e834861f2
    -- make -j5

then adding 'unused-module' to (@@ (guix build compiler) %warnings),
building, and checking all the "unused module" warnings and removing
those that were definitely unused.

guix/build/clojure-utils.scm

@@ -20,7 +20,6 @@
   #:use-module (guix build utils)
   #:use-module (ice-9 ftw)
   #:use-module (ice-9 match)
-  #:use-module (ice-9 regex)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-8)
   #:use-module (srfi srfi-26)