devserver: Deprecate --remote_payload and --urlbase

--remote_payload flag was used to run a devserver (e.g. locally) and get
update payloads from another running devserver (lab).

We have deprecated the --remote_payload use case from autotests per
crrev.com/c/1692004 and cherry-picked it all the way back to M74 (even
passed stable). Now we can deprecate it from devserver too.

BUG=chromium:980362
TEST=unittests

Change-Id: I040566d769c1a4baa73da770734a98282444ada9
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/1700392
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: David Haddock <dhaddock@chromium.org>
Commit-Queue: Amin Hassani <ahassani@chromium.org>
3 files changed