testing: Fix Docker deprecation warnings (elastic#40734)

* testing: Fix Docker deprecation warnings

I stumbled upon some warnings when trying to start the integration testing
environment. The errors don't cause any harm but they pollute the output of
the tool. Errors include:

	WARN[0000] /home/mauri870/git/elastic/beats/testing/environments/snapshot.yml: the attribute `version` is obsolete, it will be ignored, please remove it to avo
id potential confusion
	WARN[0000] /home/mauri870/git/elastic/beats/testing/environments/local.yml: the attribute `version` is obsolete, it will be ignored, please remove it to avoid
potential confusion

	WARN: MaintainerDeprecated: Maintainer instruction is deprecated in favor of using label (line 4)

testing/environments/Dockerfile

@@ -1,7 +1,6 @@
 # Basic debian file with curl, wget and nano installed to fetch files
 # an update config files
 FROM debian:latest
-MAINTAINER Nicolas Ruflin <[email protected]>
 
 RUN apt-get update && \
     apt-get install -y curl nano wget zip && \

testing/environments/local.yml

@@ -2,7 +2,6 @@
 # This is useful for testing locally with a full elastic stack setup.
 # All services can be reached through localhost like localhost:5601 for Kibana
 # This is not used for CI as otherwise ports conflicts could happen.
-version: '2.3'
 services:
   kibana:
     ports:

testing/environments/snapshot.yml

@@ -1,6 +1,5 @@
 # This should start the environment with the latest snapshots.
 
-version: '2.3'
 services:
   elasticsearch:
     image: docker.elastic.co/elasticsearch/elasticsearch:8.16.0-07587139-SNAPSHOT