test: remove the version compatibility tests

The x-plugins version is now kept in sync with the elasticsearch version and the
VersionCompatibilityTests just adds noise when updating versions.

Closes elastic/elasticsearch#3079
See elastic/elasticsearch#3212

Original commit: elastic/x-pack-elasticsearch@5998aa2ec0

elasticsearch/x-pack/security/src/test/java/org/elasticsearch/xpack/security/VersionCompatibilityTests.java

@@ -1,41 +0,0 @@
-/*
- * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
- * or more contributor license agreements. Licensed under the Elastic License;
- * you may not use this file except in compliance with the Elastic License.
- */
-package org.elasticsearch.xpack.security;
-
-import org.apache.lucene.util.LuceneTestCase.AwaitsFix;
-import org.elasticsearch.Version;
-import org.elasticsearch.license.XPackLicenseState;
-import org.elasticsearch.test.ESTestCase;
-
-import static org.hamcrest.CoreMatchers.is;
-
-/**
- * This class is used to keep track of changes that we might have to make once we upgrade versions of dependencies, especially
- * elasticsearch core.
- * Every change is listed as a specific assert that trips with a future version of es core, with a meaningful description that explains
- * what needs to be done.
- * <p>
- * For each assertion we should have one or more corresponding TODOs in the code points that require changes, and also a link to the
- * issue that applies the
- * required fixes upstream.
- * <p>
- * In many cases we will just have to bump the version of the assert then, unless we want to break backwards compatibility, but the idea
- * is that this class
- * helps keeping track of this and eventually making changes when needed.
- */
-@AwaitsFix(bugUrl = "does this still make sense?")
-public class VersionCompatibilityTests extends ESTestCase {
-    public void testCompatibility() {
-        /**
-         * see https://github.com/elasticsearch/elasticsearch/issues/9372 {@link XPackLicenseState}
-         * Once es core supports merging cluster level custom metadata (licenses in our case), the tribe node will see some license
-         * coming from the tribe and everything will be ok.
-         *
-         */
-        assertThat("Remove workaround in LicenseService class when es core supports merging cluster level custom metadata",
-                   Version.CURRENT.equals(Version.V_5_0_0_alpha5), is(true));
-    }
-}