[test] Deprecate PMDTestRunner and RuleTestRunner

They were only needed for JUnit4

pmd-test/src/main/java/net/sourceforge/pmd/testframework/PMDTestRunner.java

@@ -36,7 +36,10 @@ import org.junit.runners.model.InitializationError;
  * ...
  * }
  * </pre>
+ *
+ * @deprecated This is not needed anymore with JUnit5. Just extend from {@link SimpleAggregatorTst}.
  */
+@Deprecated
 public class PMDTestRunner extends Runner implements Filterable, Sortable {
     private final Class<? extends SimpleAggregatorTst> klass;
     private final RuleTestRunner ruleTests;

pmd-test/src/main/java/net/sourceforge/pmd/testframework/RuleTestRunner.java

@@ -33,7 +33,9 @@ import net.sourceforge.pmd.Rule;
  * TestRules.
  *
  * @author Andreas Dangel
+ * @deprecated This is not needed anymore with JUnit5
  */
+@Deprecated
 public class RuleTestRunner extends ParentRunner<TestDescriptor> {
     private ConcurrentMap<TestDescriptor, Description> testDescriptions = new ConcurrentHashMap<>();
     private final RuleTst instance;