ci: remove bazel job from Travis (#22170)

This saves us an executor on Travis.

Note that we still do a bazel build on travis when we run the integration tests under e2e_2.

We expect that CircleCI is the only place we'll ever consume bazel-built artifacts.

PR Close #22170

scripts/ci/test-bazel.sh

@@ -1,5 +0,0 @@
-#!/usr/bin/env bash
-
-set -u -e -o pipefail
-
-bazel build --config=ci packages/...

scripts/ci/test.sh

@@ -46,7 +46,4 @@ case ${CI_MODE} in
   aio_e2e)
     ${thisDir}/test-aio-e2e.sh
     ;;
-  bazel)
-    ${thisDir}/test-bazel.sh
-    ;;
 esac