tdf#113353 gtk2: No decoration for floating toolbars

Some window managers need this explicit setting.

Change-Id: I007f066e29002d8988132f72ef55fbe3b679fa8c
Reviewed-on: https://gerrit.libreoffice.org/43697Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

vcl/unx/gtk/gtksalframe.cxx

@@ -1216,6 +1216,7 @@ void GtkSalFrame::Init( SalFrame* pParent, SalFrameStyleFlags nStyle )
         {
             eType = GDK_WINDOW_TYPE_HINT_TOOLBAR;
             lcl_set_accept_focus( GTK_WINDOW(m_pWindow), false, true );
+            gtk_window_set_decorated( GTK_WINDOW(m_pWindow), false );
         }
         if( (nStyle & SalFrameStyleFlags::PARTIAL_FULLSCREEN )
             && getDisplay()->getWMAdaptor()->isLegacyPartialFullscreen() )