gnu: emacs-bash-completion: Improve package style.

* gnu/packages/emacs-xyz.scm (emacs-bash-completion)[arguments]<#:phases>:
Remove trailing #T.  Use G-expressions.  Use SEARCH-INPUT-FILE.

gnu/packages/emacs-xyz.scm

@@ -15958,18 +15958,17 @@ (define-public emacs-bash-completion
       (inputs (list bash))
       (build-system emacs-build-system)
       (arguments
-      `(#:phases
-        (modify-phases %standard-phases
+       (list
+        #:phases
+        #~(modify-phases %standard-phases
             (add-after 'unpack 'make-git-checkout-writable
               (λ _
-              (for-each make-file-writable (find-files "."))
-              #t))
+                (for-each make-file-writable (find-files "."))))
             (add-before 'install 'configure
               (lambda* (#:key inputs #:allow-other-keys)
-              (let ((bash (assoc-ref inputs "bash")))
                 (emacs-substitute-variables "bash-completion.el"
-                  ("bash-completion-prog" (string-append bash "/bin/bash"))))
-              #t)))))
+                  ("bash-completion-prog"
+                   (search-input-file inputs "/bin/bash"))))))))
       (home-page "https://github.com/szermatt/emacs-bash-completion")
       (synopsis "Bash completion for the shell buffer")
       (description