I'm sorry but you can't delete those addresses. That's a "helpful" feature by Apple that, well, isn't. At the present time (and since the start of the iPad) there is no way to remove those addresses from a stock iPad. The best you can hope for is for them to get pushed further down the recommendations list because you don't use them.
We keep hoping for a change but so far, no luck. Again, sorry.
Marilyn