org.el: Don't bind C-<up> and C-<down> to `org-element-backward/forward'.

* org.el (org-mode-map): Don't bind C-<up> and C-<down> to
`org-element-backward/forward' as these functions stops when
there is no element of the same type before/after point.  It
is useful to navigate with `forward/backward-paragraph' with
no stop in most cases.

lisp/org.el

@@ -17852,8 +17852,6 @@ BEG and END default to the buffer boundaries."
     (org-defkey narrow-map "e" 'org-narrow-to-element)
   (org-defkey org-mode-map "\C-xne" 'org-narrow-to-element))
 (org-defkey org-mode-map "\C-\M-t"  'org-element-transpose)
-(org-defkey org-mode-map [(control down)]  'org-element-forward)
-(org-defkey org-mode-map [(control up)]    'org-element-backward)
 (org-defkey org-mode-map "\M-}"    'org-element-forward)
 (org-defkey org-mode-map "\M-{"    'org-element-backward)
 (org-defkey org-mode-map "\C-c\C-^"   'org-element-up)