[ozone/wayland] Get rid of MockWaylandXkbKeyboardLayoutEngine

Now that both chrome and unittests use WaylandXkbKeyboardLayoutEngine,
we can get rid of MockWaylandXkbKeyboardLayoutEngine altogether.

BUG=578890

Change-Id: I034f44900d5051f11b234057eb4afb5e45f8bc84
Reviewed-on: https://chromium-review.googlesource.com/868670
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#530536}
7 files changed