fix(ci): remove explicit DOCKER_HOST environment variable

The explicit DOCKER_HOST configuration is no longer needed as docker-java now uses its default configuration

Author: j5ik2o

.github/workflows/ci.yml

@@ -51,7 +51,6 @@ jobs:
       JVM_OPTS:  -Xms2048M -Xmx2048M -Xss6M -XX:ReservedCodeCacheSize=256M -Dfile.encoding=UTF-8
       AWS_REGION: ap-northeast-1
       TEST_TIME_FACTOR: 5
-      DOCKER_HOST: unix:///var/run/docker.sock
     steps:
       - uses: actions/[email protected]
         with: