node.c: removed duplicate node_buffer_t definition

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60495 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

node.c

@@ -1217,11 +1217,11 @@ typedef struct node_buffer_elem_struct {
     NODE buf[1];
 } node_buffer_elem_t;
 
-typedef struct node_buffer_struct {
+struct node_buffer_struct {
     long idx, len;
     node_buffer_elem_t *head;
     node_buffer_elem_t body;
-} node_buffer_t;
+};
 
 node_buffer_t *
 rb_node_buffer_new()