Unset key binding in emacs

Question

For example, in the codes of zen-coding, the "C-j" shadows the normal behavior of "C-j" (newline-and-indent)

(define-key zencoding-mode-keymap (kbd "C-j") 'zencoding-expand-line)

Then how can I unset this keybinding and use C-j for newline-and-indent again?

I tried this, but it doesn't work:

(add-hook 'html-mode-hook
          (lambda ()
            (progn
              (zencoding-mode)
              (local-set-key (kbd "C-j") 'newline-and-indent))))

Does anyone have ideas about this?