chromeos: remove debugd GetWiMaxStatus binding

WiMAX support is deprecated along with daisy. This CL removes the
wimax-status entry under chrome://system and the corresponding debugd
GetWiMaxStatus D-Bus binding.

Bug: 954635
Test: Verify that chrome://system no longer fetches wimax-status from debugd.
Change-Id: Iafa7900dcee718593ef7cbb223d51bec2986d32f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1577631
Auto-Submit: Ben Chan <benchan@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653399}