Revert "gnu: man-db: Embed absolute reference to 'preconv'."

This change broke `man` when invoked outside a `guix environment`.

This reverts commit 296551a2e9.

gnu/packages/man.scm

@@ -5,7 +5,6 @@
 ;;; Copyright © 2015 Alex Kost <alezost@gmail.com>
 ;;; Copyright © 2015, 2016 Efraim Flashner <efraim@flashner.co.il>
 ;;; Copyright © 2017, 2018 Tobias Geerinckx-Rice <me@tobias.gr>
-;;; Copyright © 2018 Marius Bakke <mbakke@fastmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -81,19 +80,11 @@ a flexible and convenient way.")
                               (string-append "#!" (which "sh")))))
                          (remove file-is-directory?
                                  (find-files "src/tests" ".*"))))))
-         (add-after 'unpack 'patch-absolute-paths
+         (add-after 'unpack 'patch-iconv-path
            (lambda* (#:key inputs #:allow-other-keys)
              (substitute* "src/man.c"
                (("\"iconv\"")
                 (string-append "\"" (which "iconv") "\"")))
-             ;; Embed an absolute reference to "preconv", otherwise it
-             ;; falls back to searching in PATH and ultimately fails
-             ;; to render unicode data (see <https://bugs.gnu.org/30785>).
-             (substitute* "lib/encodings.c"
-               (("groff_preconv = NULL")
-                (string-append "groff_preconv = \""
-                               (assoc-ref inputs "groff-minimal")
-                               "/bin/preconv\"")))
              #t)))
        #:configure-flags
        (let ((groff (assoc-ref %build-inputs "groff"))