minor psyntax refactors

* module/ice-9/psyntax.scm (syntax-type): Remove redundant lexical
  case.
  (syntax-rules, define-syntax-rule): Use `_' instead of `dummy' for the
  keyword.

* module/ice-9/boot-9.scm (define-syntax-rule): Remove redundant
  definition.

module/ice-9/boot-9.scm

@@ -410,20 +410,6 @@ If there is no handler at all, Guile prints an error and then exits."
 ;; The binding for `macroexpand' has now been overridden, making psyntax the
 ;; expander now.
 
-(define-syntax define-syntax-rule
-  (lambda (x)
-    (syntax-case x ()
-      ((_ (name . pattern) template)
-       #'(define-syntax name
-           (syntax-rules ()
-             ((_ . pattern) template))))
-      ((_ (name . pattern) docstring template)
-       (string? (syntax->datum #'docstring))
-       #'(define-syntax name
-           (syntax-rules ()
-             docstring
-             ((_ . pattern) template)))))))
-
 (define-syntax and
   (syntax-rules ()
     ((_) #t)

module/ice-9/psyntax.scm

@@ -1115,7 +1115,6 @@
                  (b (lookup n r mod))
                  (type (binding-type b)))
             (case type
-              ((lexical) (values type (binding-value b) e w s mod))
               ((global) (values type n e w s mod))
               ((macro)
                (if for-car?
@@ -2652,7 +2651,7 @@
            #((macro-type . syntax-rules)
              (patterns pattern ...))
            (syntax-case x (k ...)
-             ((dummy . pattern) #'template)
+             ((_ . pattern) #'template)
              ...)))
       ((_ (k ...) docstring ((keyword . pattern) template) ...)
        (string? (syntax->datum #'docstring))
@@ -2662,7 +2661,7 @@
            #((macro-type . syntax-rules)
              (patterns pattern ...))
            (syntax-case x (k ...)
-             ((dummy . pattern) #'template)
+             ((_ . pattern) #'template)
              ...))))))
 
 (define-syntax define-syntax-rule