Remove WORKSPACE_WINDOW_STATE_WINDOW_OVERLAPS_SHELF and related code

Shelf no longer becomes transparent when on overlapped windows,
so we can remove this.

Bug: 912191
Test: updated existing tests to reflect the change.
Change-Id: I5bd31fb131703e4ba779b2444838e87d31358192
Reviewed-on: https://chromium-review.googlesource.com/c/1399047
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Chris Palmer <palmer@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621070}
16 files changed