wacom: Set several notebooks' show-border property to FALSE

Since GTK+ commit 05b1ea84b, this hint is used in GtkNotebook to add
a GTK_STYLE_CLASS_FRAME when rendering the notebook frame, so the theme
renders those frame-alike. As it's not what we want for the wacom panel,
set show-border to FALSE on all GtkNotebooks.

https://bugzilla.gnome.org/show_bug.cgi?id=710709