gnu: emacs-deadgrep: Improve package style.

* gnu/packages/emacs-xyz.scm (emacs-deadgrep)[arguments]: Use G-expressions.
<#:phases>: Use SEARCH-INPUT-FILE instead of ASSOC-REF.

gnu/packages/emacs-xyz.scm

@@ -23875,22 +23875,21 @@ accept and reject GitHub pull requests.")
         (base32
          "0bwf8gsqw7hsmacqd34piwgv066ijfclmxaigkvhvpac0lpsmi79"))))
     (build-system emacs-build-system)
-    (inputs (list ripgrep))
-    (propagated-inputs
-     (list emacs-dash emacs-s emacs-spinner))
     (arguments
-     `(#:phases
-       (modify-phases %standard-phases
+     (list
+      #:phases
+      #~(modify-phases %standard-phases
           (add-after 'unpack 'configure
             (lambda* (#:key inputs #:allow-other-keys)
-             (let ((ripgrep (assoc-ref inputs "ripgrep")))
-               ;; .el is read-only in git.
-               (make-file-writable "deadgrep.el")
-               ;; Specify the absolute file names of rg so that everything
+              (let ((ripgrep (search-input-file inputs "/bin/rg")))
+                ;; Specify the absolute file name of rg so that everything
                 ;; works out-of-the-box.
                 (emacs-substitute-variables "deadgrep.el"
-                 ("deadgrep-executable"
-                  (string-append ripgrep "/bin/rg")))))))))
+                  ("deadgrep-executable" ripgrep))))))))
+    (inputs
+     (list ripgrep))
+    (propagated-inputs
+     (list emacs-dash emacs-s emacs-spinner))
     (home-page "https://github.com/Wilfred/deadgrep")
     (synopsis "Frontend for @code{ripgrep}")
     (description "This package provides an Emacs interface for performing