gnu: Use 'search-input-directory' and 'search-input-file' where appropriate.

This changes some of the remaining uses of this idiom:

  (string-append (assoc-ref inputs "LABEL") "FILE")

to one of:

  (search-input-file inputs "FILE")
  (search-input-directory inputs "FILE")

* gnu/packages/axoloti.scm (axoloti-patcher): Use
'search-input-directory'.
(axoloti-patcher-next): Likewise.
* gnu/packages/bioinformatics.scm (java-picard): Likewise.
* gnu/packages/bootloaders.scm (grub-hybrid): Likewise.
(u-boot-puma-rk3399): Likewise.
(u-boot-rock64-rk3328): Likewise.
(u-boot-firefly-rk3399): Likewise.
(u-boot-rockpro64-rk3399): Likewise.
(u-boot-pinebook-pro-rk3399): Likewise.
* gnu/packages/cran.scm (r-shiny): Likewise.
(r-shinytree): Likewise.
* gnu/packages/education.scm (anki): Likewise.
* gnu/packages/emacs-xyz.scm (emacs-flycheck-grammalecte): Likewise.
(emacs-rime): Likewise.
* gnu/packages/emulators.scm (dolphin-emu): Likewise.
* gnu/packages/games.scm (bsd-games): Likewise.
(seahorse-adventures): Likewise.
(einstein): Likewise.
* gnu/packages/gimp.scm (gimp-fourier): Likewise.
* gnu/packages/gnome.scm (gspell): Likewise.
* gnu/packages/guile-xyz.scm (guile-libyaml): Likewise.
* gnu/packages/java.scm (icedtea-7): Likewise.
* gnu/packages/language.scm (nimf): Likewise.
* gnu/packages/lxde.scm (spacefm): Likewise.
* gnu/packages/mail.scm (claws-mail): Likewise.
* gnu/packages/netpbm.scm (netpbm): Likewise.
* gnu/packages/networking.scm (blueman): Likewise.
* gnu/packages/scheme.scm (scm): Likewise.
* gnu/packages/security-token.scm (python-fido2): Likewise.
* gnu/packages/syndication.scm (rtv): Likewise.
* gnu/packages/tls.scm (acme-client): Likewise.
* gnu/packages/web.scm (netsurf): Likewise.
* gnu/packages/wine.scm (wine-staging): Likewise.
* gnu/packages/wxwidgets.scm (wxwidgets): Likewise.

gnu/packages/lxde.scm

@@ -6,7 +6,7 @@
 ;;; Copyright © 2017 Brendan Tildesley <mail@brendan.scot>
 ;;; Copyright © 2018–2021 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;; Copyright © 2018 ison <ison@airmail.cc>
-;;; Copyright © 2018, 2019 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2018, 2019, 2021 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2018 Ricardo Wurmus <rekado@elephly.net>
 ;;; Copyright © 2019 Meiyo Peng <meiyo@riseup.net>
 ;;;
@@ -370,8 +370,7 @@ with freedesktop.org standard.")
                #t)))
          (add-after 'patch-share-dirs 'patch-mime-dirs
            (lambda* (#:key inputs #:allow-other-keys)
-             (let* ((mime (string-append (assoc-ref inputs "shared-mime-info")
-                                         "/share/mime")))
+             (let* ((mime (search-input-directory inputs "/share/mime")))
                (with-directory-excursion "src"
                  (substitute* '("mime-type/mime-type.c" "ptk/ptk-file-menu.c")
                    (("/usr(/local)?/share/mime") mime)))