Remove the Navigator buttons below the scrollbar in Writer

Discussion was here: http://nabble.documentfoundation.org/Libreoffice-ux-advise-Remove-the-Navigator-button-below-the-scrollbar-in-Writer-td4083097.html

Change-Id: I04b33a8e992c87b8e7519dc62c208e6dc116f8e1
Reviewed-on: https://gerrit.libreoffice.org/6045
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>
Tested-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>