I would recommend also unsetting block name "wishlist.sharing" as without doing so the wishlist can still be reached by url [http://www.yourmagentowebsite.com/wishlist/index/share/1234/][1] and could be exploited by spammers (1234 is wishlist ID). 

Comment out the following in wishlist.xml like so:

    <!--<block type="wishlist/customer_sharing" name="wishlist.sharing" template="wishlist/sharing.phtml" /> -->

or add this in your local.xml:

    <wishlist_index_share translate="label">
        <reference name="my.account.wrapper">
            <action method="unsetChild"><name>wishlist.sharing</name></action>
        </reference>   
    </wishlist_index_share>

  [1]: http://www.yourmagentowebsite.com/wishlist/index/share/1234/