Remove org-install it is deprecated

It was causing a warning every time emacs started.
Remove `:autoloads nil' from org-mode recipe

Per jd's suggestion on github,[1] I verified that this can be removed.

After cloning my repo into /tmp/el-get/el-get, I started emacs with
the following bare-bones .emacs file:

    (add-to-list 'load-path "/tmp/el-get/el-get")
    (setq el-get-dir "/tmp/el-get/")
    (require 'el-get)
    (el-get 'sync '(org-mode))

and everything performed as expected when a new Org file was opened.

[1] https://github.com/dimitri/el-get/pull/936#issuecomment-9692746.
Merge pull request #936 from rdparker/topic/cleanup-org-mode

Remove org-install it is deprecated