build: Remove references to the 'nix-hash' program.

* configure.ac: Remove check for 'nix-hash'.
* tests/base32.scm (%nix-hash, %have-nix-hash?): Remove.
("sha256 & bytevector->nix-base32-string"): Remove test.
* build-aux/pre-inst-env.in: Do not set 'NIX_HASH' environment
variable.

tests/base32.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2015 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013, 2015, 2020 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -23,26 +23,12 @@
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-64)
-  #:use-module (ice-9 rdelim)
-  #:use-module (ice-9 popen)
   #:use-module (ice-9 match)
   #:use-module (rnrs bytevectors)
   #:use-module (rnrs io ports))
 
 ;; Test the (guix base32) module.
 
-(define %nix-hash
-  (or (and=> (getenv "NIX_HASH")
-             (match-lambda
-              ("" #f)
-              (val val)))
-      "nix-hash"))
-
-(define %have-nix-hash?
-  ;; Note: Use `system', not `system*', because of <http://bugs.gnu.org/13166>.
-  (false-if-exception
-   (zero? (system (string-append %nix-hash " --version")))))
-
 (test-begin "base32")
 
 (test-assert "bytevector->base32-string"
@@ -85,19 +71,4 @@
     (nix-base32-string->bytevector
      (string-append (make-string 51 #\a) "e"))))
 
-;; The following test requires `nix-hash' in $PATH.
-(unless %have-nix-hash?
-  (test-skip 1))
-
-(test-assert "sha256 & bytevector->nix-base32-string"
-  (let ((file (search-path %load-path "tests/test.drv")))
-    (equal? (bytevector->nix-base32-string
-             (sha256 (call-with-input-file file get-bytevector-all)))
-            (let* ((c (format #f "~a --type sha256 --base32 --flat \"~a\""
-                              %nix-hash file))
-                   (p (open-input-pipe c))
-                   (l (read-line p)))
-              (close-pipe p)
-              l))))
-
 (test-end)