The following lines were added (+) and removed (-):
1. Change the value 'HKEY_CURRENT_USER\SOFTWARE\Classes\CLSID\{E31EA727-12ED-4702-820C-4B6445F28E1A}\System.IsPinnedToNamespaceTree' to 0. This should hide the icon, but it still will come back since Dropbox automatically resets the value back to 1 after a restart.2. To avoid the automatic resets, right click on the folder '{E31EA727-12ED-4702-820C-4B6445F28E1A}' in the left part and select 'Permissions...' and simply disallow the full access. As soon as you hit OK this should hide the folder's content in the registry, if you want to see the content again, re-allow the access (but this also allows Dropbox to reset the value and hence, to show the icon again).source: https://www.dropboxforum.com/t5/Installation-and-desktop-app/How-does-one-remove-the-Dropbox-link-from-the-Navigation-Pane-om/td-p/93970/page/3