It's stored in the template database.
Goto the Admin CP and go to the template modify/search section. Expand the "Default Templates", scroll to the very bottom and expand "User Control Panel Templates". Look for the template called "usercp_profile". Then look for the code
<tr>
<td colspan="3"><span class="smalltext">$lang->website_url</span></td>
</tr>
<tr>
<td colspan="3"><input type="text" name="website" size="25" maxlength="75" value="$user[website]" /></td>
</tr>
You should be able to delete that to remove the box.
For techie information it's template with tid 63, and title of 'usercp_profile'.
Ahh.. I see now
dident see the EXPAND button. Shuold make it so when you click on the name, it also expands.