Remove <server> block.

Useless for this IT, and currently triggers a failure in CI.

Should help solve https://builds.apache.org/job/maven-scm/830/console failure. 
Jenkins slave seems to have a special security settings that currently makes it fail (see https://builds.apache.org/job/maven-scm/ws/maven-scm-plugin/target/it/scm-741-validate-scm-url-matches-working-copy/build.log for details).