ci(docs-infra): move AIO preview deployment to CircleCI

Now instead of pushing the AIO build artifacts to the preview server
from inside a Travis job, the artifacts are built and hosted on the
CircleCI infrastructure. The preview server will then pull these
down after being triggered by a CircleCI build webhook.

# Conflicts:
#	.circleci/config.yml

scripts/ci/build.sh

@@ -25,16 +25,6 @@ if [[ ${CI_MODE:-} == "aio" ]]; then
   (
     cd "`dirname $0`/../../aio"
     yarn build
-
-    # If this is a PR for angular/angular@master or angular/angular@<stable-branch>, deploy a
-    # snapshot for previewing early (if preconditions are met) regardless of the test outcome.
-    if [[ ${TRAVIS_REPO_SLUG} == "angular/angular" ]] &&
-       ([[ $TRAVIS_BRANCH == "master" ]] || [[ $TRAVIS_BRANCH == $STABLE_BRANCH ]]) &&
-       [[ $TRAVIS_PULL_REQUEST != "false" ]]; then
-      travisFoldStart "deploy.aio.pr-preview"
-        yarn deploy-preview --skip-build
-      travisFoldEnd "deploy.aio.pr-preview"
-    fi
   )
   travisFoldEnd "build.aio"
   exit 0;