you mean the link that appears on your dreamwidth post that refers to the LJ post? if you go into your account settings and click on the other sites tab, you'll see a link in the 'Details' column. click that and then uncheck the ticky box next to 'Display Cross Post Links'. that field will no longer appear in your metadata.

it's an all or nothing thing, so none of your posts will feature a link for that account. if you only want to remove it for some entries then you can leave that option ticked and just delete the link on those particular entries individually.

hope this helps.