Remove ash::kTabDroppedWindowStateTypeKey

This window property was introduced at crrev.com/591079 to support
some behaviors of tab-dragging for Mash. Now it's not necessary.

Bug: 958116
Test: ash_unittests / interactive_ui_tests
Change-Id: I4cf6eca74f2e4c81de802fe0ef06b8fbe41593f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1595028
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Jun Mukai <mukai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#657014}
6 files changed