substitute: Rename cache directory from "substitute-binary" to "substitute".

* guix/scripts/substitute.scm (%narinfo-cache-directory): Change
  "substitute-binary" to "substitute".
* tests/store.scm ("substitute query"): Likewise.
* tests/substitute.scm (call-with-narinfo): Likewise.

guix/scripts/substitute.scm

@@ -69,8 +69,8 @@
 (define %narinfo-cache-directory
   ;; A local cache of narinfos, to avoid going to the network.
   (or (and=> (getenv "XDG_CACHE_HOME")
-             (cut string-append <> "/guix/substitute-binary"))
+             (cut string-append <> "/guix/substitute"))
-      (string-append %state-directory "/substitute-binary/cache")))
+      (string-append %state-directory "/substitute/cache")))
 
 (define %allow-unauthenticated-substitutes?
   ;; Whether to allow unchecked substitutes.  This is useful for testing

tests/store.scm

@@ -372,7 +372,7 @@
         ;; Remove entry from the local cache.
         (false-if-exception
          (delete-file (string-append (getenv "XDG_CACHE_HOME")
-                                     "/guix/substitute-binary/"
+                                     "/guix/substitute/"
                                      (store-path-hash-part o))))
 
         ;; Make sure 'guix substitute' correctly communicates the above

tests/substitute.scm

@@ -132,7 +132,7 @@ a file for NARINFO."
                                                 "GUIX_BINARY_SUBSTITUTE_URL"))
                                   uri-path))
         (cache-directory   (string-append (getenv "XDG_CACHE_HOME")
-                                          "/guix/substitute-binary/")))
+                                          "/guix/substitute/")))
     (dynamic-wind
       (lambda ()
         (when (file-exists? cache-directory)