services: polkit: Use the right executable name for PAM.

* gnu/services/desktop.scm (%polkit-pam-services): Change "polkit-1" to
  "polkitd", which is the actual name of the executable.

gnu/services/desktop.scm

@@ -424,7 +424,7 @@ (define %polkit-accounts
          (shell "/run/current-system/profile/sbin/nologin"))))
 
 (define %polkit-pam-services
-  (list (unix-pam-service "polkit-1")))
+  (list (unix-pam-service "polkitd")))
 
 (define (polkit-dmd-service polkit)
   "Return the <dmd-service> for POLKIT."