gnu: Use 'search-input-file' some more.

This patch replaces occurrences of:

  (string-append (assoc-ref %build-inputs "…") "/…")

by:

  (search-input-file %build-inputs "/…")

* doc/guix.texi (Miscellaneous Services): Use 'search-input-file' in R
Shiny example.
* gnu/packages/admin.scm (screenfetch): Use 'search-input-file'.
(ufetch): Likewise.
(hosts): Likewise.
* gnu/packages/backup.scm (dirvish): Likewise.
* gnu/packages/code.scm (colormake): Likewise.
* gnu/packages/compression.scm (makeself-safeextract): Likewise.
* gnu/packages/debug.scm (scanmem): Likewise.
* gnu/packages/education.scm (snap): Likewise.
(omnitux): Likewise.
* gnu/packages/emacs-xyz.scm (epipe): Likewise.
* gnu/packages/games.scm (openttd-opensfx): Likewise.
(openttd-openmsx): Likewise.
(openrct2-title-sequences):  Likewise.
(openrct2-objects):  Likewise.
(mrrescue):  Likewise.
(0ad-data):  Likewise.
(xonotic-data):  Likewise.
(drascula):  Likewise.
(make-lure-package):  Likewise.
(make-queen-package):  Likewise.
(sky):  Likewise.
* gnu/packages/gnome.scm (network-manager): Likewise.
* gnu/packages/gnuzilla.scm (icedove): Likewise.
* gnu/packages/guile-xyz.scm (guile-shapefile): Likewise.
* gnu/packages/hurd.scm (netdde): Likewise.
* gnu/packages/javascript.scm (js-context-menu): Likewise.
(js-commander): Likewise.
(js-xmldom-sre): Likewise.
* gnu/packages/kde-frameworks.scm (krunner): Likewise.
* gnu/packages/kodi.scm (kodi-cli): Likewise.
* gnu/packages/libreoffice.scm (hunspell-dict-pl): Likewise.
* gnu/packages/linux.scm (e2fsck/static): Likewise.
* gnu/packages/markup.scm (markdown): Likewise.
* gnu/packages/maths.scm (hdf-java): Likewise.
* gnu/packages/multiprecision.scm (libtomcrypt): Likewise.
* gnu/packages/networking.scm (batctl): Likewise.
* gnu/packages/python-xyz.scm (python-pymediainfo): Likewise.
* gnu/packages/shells.scm (fish-foreign-env): Likewise.
* gnu/packages/tex.scm (texlive-fonts-iwona): Likewise.
* gnu/packages/upnp.scm (miniupnpc): Likewise.
* gnu/packages/version-control.scm (git-annex-remote-rclone): Likewise.
* gnu/packages/virtualization.scm (qemu): Likewise.
* gnu/packages/web.scm (icedtea-web): Likewise.
* gnu/packages/wm.scm (stumpish): Likewise.

gnu/packages/admin.scm

@@ -3639,8 +3639,7 @@ you are running, what theme or icon set you are using, etc.")
                          (string-append out "/share/doc/" ,name "-" ,version))
            (substitute* (string-append out "/bin/screenfetch")
              (("/usr/bin/env bash")
-              (string-append (assoc-ref %build-inputs "bash")
-                             "/bin/bash")))
+              (search-input-file %build-inputs "/bin/bash")))
            (wrap-program
                (string-append out "/bin/screenfetch")
              `("PATH" ":" prefix
@@ -3650,8 +3649,9 @@ you are running, what theme or icon set you are using, etc.")
                                 (assoc-ref %build-inputs "xprop") "/bin"))))
            (substitute* (string-append out "/bin/screenfetch")
              (("#!#f")
-              (string-append "#!" (assoc-ref %build-inputs "bash")
-                             "/bin/bash")))))))
+              (string-append "#!"
+                             (search-input-file %build-inputs
+                                                "/bin/bash"))))))))
     (inputs
      `(("bash" ,bash)
        ("bc" ,bc)
@@ -3693,7 +3693,7 @@ everyone's screenshots nowadays.")
                   (output (assoc-ref %outputs "out"))
                   (bindir (string-append output "/bin"))
                   (docdir (string-append output "/share/doc/ufetch-" ,version))
-                  (tput (string-append (assoc-ref %build-inputs "tput") "/bin/tput")))
+                  (tput   (search-input-file %build-inputs "/bin/tput")))
              (install-file (string-append source "/LICENSE") docdir)
              (setenv "PATH" (string-append (assoc-ref %build-inputs "bash") "/bin"))
              (mkdir-p bindir)
@@ -4491,7 +4491,7 @@ text table representation to stdout.")
                            "\nPATH=" (getenv "PATH"))))
          ;; check phase
          (setenv "TERM" "linux") ;set to tty for test
-         (invoke (string-append (assoc-ref %build-inputs "bats") "/bin/bats")
+         (invoke (search-input-file %build-inputs "/bin/bats")
                  "test")
          ;; install phase
          (install-file "hosts" (string-append %output "/bin"))