Remove all links from the navigation bar.

It's not possible to the contact to become a mailto: link as they don't
work in QtAssistant.
Refs #9761

Code/Mantid/docs/conf-qthelp.py

@@ -17,10 +17,6 @@ html_theme_options = {
     'navbar_site_name': "Mantid",
     # Add links to the nav bar. Third param of tuple is true to create absolute url.
     'navbar_links': [
-        ("Home", "http://www.mantidproject.org", True),
-        ("Download", "http://download.mantidproject.org", True),
-        ("Documentation", "http://www.mantidproject.org/Documentation", True),
-        ("Contact Us", "http://www.mantidproject.org/Contact", True),
     ],
     # Do not show the "Show source" button.
     'source_link_position': "no",