Drop obsolete Travis build.

.travis.yml

@@ -1,29 +0,0 @@
-# Licensed to the Apache Software Foundation (ASF) under one or more
-# contributor license agreements.  See the NOTICE file distributed with
-# this work for additional information regarding copyright ownership.
-# The ASF licenses this file to You under the Apache License, Version 2.0
-# (the "License"); you may not use this file except in compliance with
-# the License.  You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-language: java
-
-matrix:
-  include:
-    - jdk: openjdk8
-    - jdk: openjdk11
-    - jdk: openjdk16
-    - jdk: openjdk-ea
-  allow_failures:
-    - jdk: openjdk-ea
-script:
-  - mvn
-after_success:
-  - mvn -B -V clean test jacoco:report coveralls:report -Ptravis-jacoco --no-transfer-progress