Remove bootstrap.memory_lock from elasticsearch-7.x-scenario

ES 7.16+ from docker.elastic.co enforces memory lock strictly and
exits when ulimits are not set, causing the container to crash and
its hostname to become unresolvable (UnknownHostException).

Author: wu-sheng

test/plugin/scenarios/elasticsearch-7.x-scenario/configuration.yml

@@ -30,6 +30,5 @@ dependencies:
     environment:
     - cluster.name=docker-node
     - xpack.security.enabled=false
-    - bootstrap.memory_lock=true
     - "ES_JAVA_OPTS=-Xms512m -Xmx512m"
     - discovery.type=single-node