services: system: Initial entries are non-monadic.

* gnu/system.scm (operating-system-directory-base-entries): Return a
regular, non-monadic value.
* gnu/services.scm (system-derivation): Adjust accordingly.
* gnu/system/linux-container.scm (container-essential-services): Likewise.

gnu/services.scm

@@ -318,11 +318,10 @@ This is a shorthand for (map (lambda (svc) ...) %base-services)."
 ;;; Core services.
 ;;;
 
-(define (system-derivation mentries mextensions)
+(define (system-derivation entries mextensions)
   "Return as a monadic value the derivation of the 'system' directory
 containing the given entries."
-  (mlet %store-monad ((entries    mentries)
-                      (extensions (mapm/accumulate-builds identity
+  (mlet %store-monad ((extensions (mapm/accumulate-builds identity
                                                           mextensions)))
     (lower-object
      (file-union "system"

gnu/system.scm

@@ -506,11 +506,10 @@ value of the SYSTEM-SERVICE-TYPE service."
                    (hooks (list linux-module-database))))
          (initrd  (operating-system-initrd-file os))
          (params  (operating-system-boot-parameters-file os)))
-    (with-monad %store-monad
-      (return `(("kernel" ,kernel)
-                ("parameters" ,params)
-                ("initrd" ,initrd)
-                ("locale" ,locale))))))   ;used by libc
+    `(("kernel" ,kernel)
+      ("parameters" ,params)
+      ("initrd" ,initrd)
+      ("locale" ,locale))))   ;used by libc
 
 (define (operating-system-default-essential-services os)
   "Return the list of essential services for OS.  These are special services

gnu/system/linux-container.scm

@@ -1,6 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2015 David Thompson <davet@gnu.org>
-;;; Copyright © 2016, 2017, 2019 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2016, 2017, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2019 Arun Isaac <arunisaac@systemreboot.net>
 ;;; Copyright © 2020 Efraim Flashner <efraim@flashner.co.il>
 ;;;
@@ -53,9 +53,7 @@ from OS that are needed on the bare metal and not in a container."
             (operating-system-default-essential-services os)))
 
   (cons (service system-service-type
-                 (let ((locale (operating-system-locale-directory os)))
-                   (with-monad %store-monad
-                     (return `(("locale" ,locale))))))
+                 `(("locale" ,(operating-system-locale-directory os))))
         ;; If network is to be shared with the host, remove network
         ;; configuration files from etc-service.
         (if shared-network?