Drop region parameter to Unbounded, as it can be done without.

Drop region parameter to Unbounded, as it can be done without.

Unbounded is defined in terms of None any Any,
which don't require an explicit zone.
Switching Unbounded to be the same.

BUG= None
TEST= trybots
R= titzer@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/1322003002

Cr-Commit-Position: refs/heads/master@{#30482}