GDK W32: transient Z-order rollback

LRN requested to merge lrn/gtk:w32-transient-ordering-rollback into gtk-3-24

Roll back the commit that added NOOWNERZORDER everywhere (but keep the one that added it for temp windows). Then remove restacking functions, as they introduce bugs (cause sontaneous reordering among transients, for example) and only existed because GTK was trying to emulate WM quirks from non-Windows WMs.

Fixes #2045 (closed) and #2439 (closed)

A simpler alternative for !1738 (closed)

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