services: dmd: Strip the default list of modules.

* gnu/services/dmd.scm (%default-imported-modules): Remove (gnu build
file-systems).
(%default-modules): Likewise, and remove (ice-9 ftw).
* gnu/services/base.scm (file-system-service-type): Add 'modules' and
'imported-modules' fields.

gnu/services/base.scm

@@ -223,7 +223,14 @@ FILE-SYSTEM."
                   (chdir "/")
 
                   (umount #$target)
-                  #f)))))))
+                  #f))
+
+        ;; We need an additional module.
+        (modules `(((gnu build file-systems)
+                    #:select (check-file-system canonicalize-device-spec))
+                   ,@%default-modules))
+        (imported-modules `((gnu build file-systems)
+                            ,@%default-imported-modules)))))))
 
 (define* (file-system-service file-system)
   "Return a service that mounts @var{file-system}, a @code{<file-system>}

gnu/services/dmd.scm

@@ -107,18 +107,14 @@ service that extends DMD-ROOT-SERVICE-TYPE and nothing else."
 (define %default-imported-modules
   ;; Default set of modules imported for a service's consumption.
   '((guix build utils)
-    (guix build syscalls)
-    (gnu build file-systems)))
+    (guix build syscalls)))
 
 (define %default-modules
   ;; Default set of modules visible in a service's file.
   `((dmd service)
     (oop goops)
-    (ice-9 ftw)
     (guix build utils)
-    (guix build syscalls)
-    ((gnu build file-systems)
-     #:select (check-file-system canonicalize-device-spec))))
+    (guix build syscalls)))
 
 (define-record-type* <dmd-service>
   dmd-service make-dmd-service