treeview: Deprecated rules-hint

treeview: Deprecated rules-hint

The rules-hint property has always been a fairly bad application API, as
it set some wrong expectations for the developers; deferring to the
theme makes it impossible to design application reliably, and if this is
a usability setting we should either impose this setting on every theme,
or simply drop it.

Our own default theme does not honour the zebra striping, which makes
this function even more questionable.

In practice, usability studies on zebra striping have demonstrated that
alternating colors on a list it improves readability just as much as
clear ruling between rows, or by visually differentiating the selected
row. Zebra striping improves readability (or, at least, it does not
hinder it) on static displays, like a table on paper or a document; on a
dynamic display, like an application's UI, there are different
strategies that yield similar, if not better, results.

https://bugzilla.gnome.org/show_bug.cgi?id=733312