Remove extraneous size request

Remove extraneous size request

After “validation” (i.e., background size calculations) of some cells,
size_request() was called here to update the internally cached size of
the treeview.  Apparently not updating the sizes leads to some kind of
“inconsistency” that messes with top_row_to_dy().  In the GTK3 model for
size allocation, things are more complicated.  The treeview can’t just
go ahead and calculate its own size any more; instead it reports both a
“minimum” and a “natural” size, and it doesn’t know what size it will
actually get until size_allocate().  It may be necessary to update
top_row_to_dy() to deal with not knowing the exact size.

https://bugzilla.gnome.org/show_bug.cgi?id=691751