This reverts commit 332d1892bb.
And re-introduces the bug it was intended to fix, see:
https://lists.freedesktop.org/archives/wayland-devel/2017-December/036402.html
Reverting this because it causes harm to all xwayland clients - the
input region no longer gets adjusted when resizing windows.
start an xterm, resize it larger, you can no longer interact with the
new area of the window (including the server side decor).