(sh-mode): If there is no #!-line, use the shell

from sh-shell-file.

lisp/progmodes/sh-script.el

@@ -1297,12 +1297,7 @@ with your script for an edit-interpret-debug cycle."
 		  "rpm")))))
     (if interpreter
 	(sh-set-shell interpreter nil nil)
-      (progn
-        ;; If we don't know the shell for this file, set the syntax
-        ;; table anyway, for the user's normal choice of shell.
-        (set-syntax-table (sh-feature sh-mode-syntax-table))
-        ;; And avoid indent-new-comment-line (at least) losing.
-        (setq comment-start-skip "#+[\t ]*"))))
+      (sh-set-shell sh-shell-file nil t))
   (run-hooks 'sh-mode-hook))
 ;;;###autoload
 (defalias 'shell-script-mode 'sh-mode)