[ZOOKEEPER-4642] Remove Travis CI

.travis.yml

@@ -1,35 +0,0 @@
-language: java
-
-matrix:
-  include:
-    - os: linux
-      arch: arm64
-      jdk: openjdk11
-      install: |
-        f=$(which javac)
-        while [[ -L $f ]]; do f=$(readlink $f); done
-        export JAVA_HOME=${f%/bin/*}
-
-    - os: linux
-      arch: s390x
-      jdk: openjdk11
-
-cache:
-  directories:
-  - "$HOME/.m2"
-
-addons:
-  apt:
-    update: true
-    packages:
-      - maven
-      - libcppunit-dev
-
-script: mvn clean apache-rat:check verify -DskipTests spotbugs:check checkstyle:check -Pfull-build
-
-branches:
-  only:
-  - master
-  - branch-3.7
-  - branch-3.6
-  - branch-3.5