profile: Drop default values for check buttons

Setting an xalign of 0.5 and expecting the following setting of
draw-indicator to TRUE to neutralize it is somewhat fragile. It only
worked because GTK+ was doing redundant property notification.

Now that GTK+ uses G_PARAM_EXPLICIT_NOTIFY, it no longer works.

https://bugzilla.gnome.org/show_bug.cgi?id=732361