remove obsolete tomcat docker image from integration tests

[SylvainJuge]

What does this PR do?

Removes the tomcat 8.5.0 docker image.

When trying to pull this docker image from CLI with docker pull tomcat:8.5.0-jre8 we get the following error:

8.5.0-jre8: Pulling from library/tomcat
[DEPRECATION NOTICE] Docker Image Format v1 and Docker Image manifest version 2, schema 1 support is disabled by default and will be removed in an upcoming release. Suggest the author of docker.io/library/tomcat:8.5.0-jre8 to upgrade the image to the OCI Format or Docker Image manifest v2, schema 2. More information at https://docs.docker.com/go/deprecated-image-specs/

This docker image is being used by the co.elastic.apm.servlet.TomcatIT integration tests, which fails when run locally and in CI, but does not trigger a failure in CI, which will need proper investigation.

This 9 year old docker image is not maintained anymore, thus the simplest way to move forward is to remove it.

[JonasKunz]

We'll wait on merging this one, because this PR removes our way to reproduce the CI issue where the CI is green even though some tests (=the tomcat test) failed.

[JonasKunz]

Merging now, because the root cause of undetected CI failures has been found and will be fixed with #3952.