Revert "Allow dragging for NonClientArea (i.e. DraggableRegions)"

This reverts commit 5a98d6119a8d9499f6d64b8b80428ae3e48708ee.

Reason for revert: browser-windows get unresizable

Original change's description:
> Allow dragging for NonClientArea (i.e. DraggableRegions)
> 
> The non-client area in ProxyWindow is set through "DraggableRegions",
> and this section is used for draggability of the window (see
> https://cs.chromium.org/chromium/src/apps/ui/views/app_window_frame_view.cc?sq=package:chromium&g=0&l=196).
> 
> The same logic should be introduced on Mash, otherwise frameless
> app window can't be dragged.
> 
> Bug: 920469
> Test: ash_unittests
> Change-Id: If249d58dbf0a84aa3b333799f44f122dca04c4e6
> Reviewed-on: https://chromium-review.googlesource.com/c/1405458
> Reviewed-by: Scott Violet <sky@chromium.org>
> Commit-Queue: Jun Mukai <mukai@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#622061}

TBR=mukai@chromium.org,sky@chromium.org

Change-Id: Ib51b583478e4d74c5754d0c243708bcd6a368d66
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 920469
Reviewed-on: https://chromium-review.googlesource.com/c/1407666
Reviewed-by: Jun Mukai <mukai@chromium.org>
Commit-Queue: Jun Mukai <mukai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622189}
6 files changed