Remove dupe "Speakers" page & vsite task #5387

#5387 

From QA, @tcheng001 noticed a duplicate "Speakers" page post. Instead "Speakers" should just be the renamed "People" menu link.

#### Changes

* Remove the "Speakers" page task from vsite_preset.module, since no "Speakers" page is needed by any of our presets.
* Remove the `vsite_preset_section_speakers` task from the `og_tasks` array in the Conference preset.

Note: There is still a "Speakers" menu item which is the renamed "People" menu link. So the vsite_preset_menu_order does not need to be updated.