travis: Cut webhook config pointing at zulipbot.

We haven't actually been using this zulipbot feature for a long time
(haven't applied the `travis updates` label which it looks for.)
Rather than port the config to CircleCI, just cut it for now; we can
always add something like it back if we start using it.

.circleci/config.yml

@@ -83,8 +83,6 @@ jobs:
       #     # also /tmp/zulip-test-event-log/
       #     destination: test-reports
 
-      # TODO: notify zulipbot
-
   "xenial-python-3.5":
     docker:
       # This is built from tools/circleci/images/xenial/Dockerfile .

.travis.yml

@@ -70,9 +70,3 @@ addons:
       - moreutils
 after_success:
   - codecov
-notifications:
-  webhooks:
-    urls:
-      - https://zulip.org/zulipbot/travis
-    on_success: always
-    on_failure: always