Revert "publish: Prevent publication of non-substitutable derivation outputs."

Fixes guix/guix#2450.

This reverts commit b5745a327e, which introduced
discrepancies in how substitutes are served; in particular, narinfos of
non-substitutable items would still be served, and likewise for narinfos and
nars of dependents of non-substitutable items.

guix/scripts/publish.scm

@@ -61,7 +61,6 @@
   #:use-module (guix cache)
   #:use-module (guix ui)
   #:use-module (guix scripts)
-  #:use-module (guix derivations)
   #:use-module ((guix utils)
                 #:select (with-atomic-file-output compressed-file?))
   #:use-module ((guix build utils)
@@ -694,14 +693,11 @@ requested using POOL."
 (define* (render-nar store request store-item
                      #:key (compression %no-compression))
   "Render archive of the store path corresponding to STORE-ITEM."
-  (let* ((store-path (string-append %store-directory "/" store-item))
-         (derivations (map read-derivation-from-file
-                           (valid-derivers store store-path)))
-         (substitutable? (every substitutable-derivation? derivations)))
+  (let ((store-path (string-append %store-directory "/" store-item)))
     ;; The ISO-8859-1 charset *must* be used otherwise HTTP clients will
     ;; interpret the byte stream as UTF-8 and arbitrarily change invalid byte
     ;; sequences.
-    (if (and substitutable? (valid-path? store store-path))
+    (if (valid-path? store store-path)
         (values `((content-type . (application/x-nix-archive
                                    (charset . "ISO-8859-1")))
                   (x-nar-compression . ,compression))

tests/publish.scm

@@ -425,23 +425,6 @@ FileSize: ~a~%"
         (display "This file is not a valid store item." port)))
     (response-code (http-get (publish-uri (string-append "/nar/invalid"))))))
 
-(test-equal "non-substitutable derivation"
-  404
-  (let* ((non-substitutable
-          (run-with-store %store
-            (gexp->derivation "non-substitutable"
-                              #~(begin
-                                  (mkdir #$output)
-                                  (chdir #$output)
-                                  (call-with-output-file "foo.txt"
-                                    (lambda (port)
-                                      (display "bar" port))))
-                              #:substitutable? #f)))
-         (item (derivation->output-path non-substitutable)))
-    (build-derivations %store (list non-substitutable))
-    (response-code (http-get (publish-uri
-                              (string-append "/nar/" (basename item)))))))
-
 (test-equal "/file/NAME/sha256/HASH"
   "Hello, Guix world!"
   (let* ((data "Hello, Guix world!")