Revert "Forward-port a GtkAdjustment compatibility fix"

Revert "Forward-port a GtkAdjustment compatibility fix"

In the early 2.14.x releases, GtkAdjustment was changed to enforce
that values are restricted to the range [lower, upper - page_size].
This has always been the documented behaviour, and the recommended
practice is to set page_size to 0 when using adjustments for simple
scalar values, like in a slider or spin button.
Due to the large number of applications that are affected by this
change, the behaviour has been reverted to the old behaviour in
2.14.3, with an explicit warning that this change will be
reintroduced in 2.90.

This reverts commit e6373738fc9c53c95e467a3681fcd3426fd94d13.

https://bugzilla.gnome.org/show_bug.cgi?id=619474