store: Remove 'register-path'.

* guix/store.scm (register-path): Remove.
* guix/nar.scm: Use (guix store database).
* guix/scripts/system.scm: Likewise.
* tests/store-database.scm: Remove #:hide (register-path).
* tests/store.scm ("register-path"): Remove.

tests/store.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -777,26 +777,6 @@
              (pk 'corrupt-imported imported)
              #f)))))
 
-(test-assert "register-path"
-  (let ((file (string-append (%store-prefix) "/" (make-string 32 #\f)
-                             "-fake")))
-    (when (valid-path? %store file)
-      (delete-paths %store (list file)))
-    (false-if-exception (delete-file file))
-
-    (let ((ref (add-text-to-store %store "ref-of-fake" (random-text)))
-          (drv (string-append file ".drv")))
-      (call-with-output-file file
-        (cut display "This is a fake store item.\n" <>))
-      (register-path file
-                     #:references (list ref)
-                     #:deriver drv)
-
-      (and (valid-path? %store file)
-           (equal? (references %store file) (list ref))
-           (null? (valid-derivers %store file))
-           (null? (referrers %store file))))))
-
 (test-assert "verify-store"
   (let* ((text  (random-text))
          (file1 (add-text-to-store %store "foo" text))