environment: Use (guix search-paths).

* guix/scripts/environment.scm: Use (guix search-paths).  Fixes a
  regression introduced in e89431b.

guix/scripts/environment.scm

@@ -22,6 +22,7 @@
   #:use-module (guix derivations)
   #:use-module (guix packages)
   #:use-module (guix profiles)
+  #:use-module (guix search-paths)
   #:use-module (guix utils)
   #:use-module (guix monads)
   #:use-module (guix build utils)