some options inherited from the page plugin don't make sense

Not all the options in the UI make sense as they are currently presented:

- Items per page -- this needs to have its UI text tweaked so it can be understood that this is the number of items to load at a time
- Number of pages -- would this do anything at all?
- Number of pager links visible -- presumably this does nothing; there are no pager links. It should maybe be removed in the views_plugin_pager_infinite_scroll class?
- Tags fieldset - ditto