Remove travis.yml (#284)

This looks like it's left over from before the switch to buildkite.
The Travis tests are not run in precommit now, and I can't even tell
if they were run in PR #1.

This causes pre-commit errors in forks if folks have Travis
enabled in other projects.
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index 8b44fca..0000000
--- a/.travis.yml
+++ /dev/null
@@ -1,27 +0,0 @@
-sudo: required
-dist: trusty
-language:
-  - java
-jdk:
-  - oraclejdk8  # Building Bazel requires JDK8.
-addons:
-  apt:
-    sources:
-      - sourceline: 'deb [arch=amd64] http://storage.googleapis.com/bazel-apt stable jdk1.8'
-        key_url: 'https://storage.googleapis.com/bazel-apt/doc/apt-key.pub.gpg'
-    packages:
-      - bazel
-
-install:
-  - go get -u github.com/bazelbuild/buildifier/buildifier
-
-script:
-  # Check that all of our tools and samples build
-  - bazel clean && bazel build //...
-  # Check that all of our tests pass
-  - bazel clean && bazel test //...
-
-  # Check for issues with the format of our bazel config files.
-  - buildifier -mode=check $(find . -name BUILD -type f)
-  - buildifier -mode=check $(find . -name WORKSPACE -type f)
-  - buildifier -mode=check $(find . -name '*.bzl' -type f)