linux-container: Remove dependency on (guix utils).

Fixes a bug whereby derivations importing (gnu build linux-container),
such as the 'bitlbee' and 'tor' services, would depend on the
user's (guix config) file, which was pulled as a dependency of (guix
utils).  As a result, those derivations would vary from user to user.

* gnu/build/linux-container.scm (call-with-temporary-directory): New
procedure.

gnu/build/linux-container.scm

@@ -22,7 +22,6 @@
   #:use-module (ice-9 match)
   #:use-module (ice-9 rdelim)
   #:use-module (srfi srfi-98)
-  #:use-module (guix utils)
   #:use-module (guix build utils)
   #:use-module (guix build syscalls)
   #:use-module (gnu system file-systems)          ;<file-system>
@@ -279,6 +278,21 @@ that host UIDs (respectively GIDs) map to in the namespace."
               (_                                  ;unexpected termination
                #f)))))))))
 
+;; FIXME: This is copied from (guix utils), which we cannot use because it
+;; would pull (guix config) and all.
+(define (call-with-temporary-directory proc)
+  "Call PROC with a name of a temporary directory; close the directory and
+delete it when leaving the dynamic extent of this call."
+  (let* ((directory (or (getenv "TMPDIR") "/tmp"))
+         (template  (string-append directory "/guix-directory.XXXXXX"))
+         (tmp-dir   (mkdtemp! template)))
+    (dynamic-wind
+      (const #t)
+      (lambda ()
+        (proc tmp-dir))
+      (lambda ()
+        (false-if-exception (delete-file-recursively tmp-dir))))))
+
 (define* (call-with-container mounts thunk #:key (namespaces %namespaces)
                               (host-uids 1) (guest-uid 0) (guest-gid 0))
   "Run THUNK in a new container process and return its exit status.