Get rid of warnings, cleanup (#19)

Changes:
* get rid of unused Plexus XML and properties
* slight updates
* use jar-no-fork
* remove prerequisite, this is not a maven-plugin
diff --git a/maven-plugin-testing-harness/pom.xml b/maven-plugin-testing-harness/pom.xml
index 62ad998..83a190c 100644
--- a/maven-plugin-testing-harness/pom.xml
+++ b/maven-plugin-testing-harness/pom.xml
@@ -68,7 +68,7 @@
     <dependency>
       <groupId>org.codehaus.plexus</groupId>
       <artifactId>plexus-archiver</artifactId>
-      <version>4.2.4</version>
+      <version>4.2.5</version>
     </dependency>
   </dependencies>
 
@@ -82,7 +82,7 @@
         <executions>
           <execution>
             <goals>
-              <goal>jar</goal>
+              <goal>jar-no-fork</goal>
             </goals>
           </execution>
         </executions>
diff --git a/maven-plugin-testing-harness/src/main/resources/META-INF/plexus/components.xml b/maven-plugin-testing-harness/src/main/resources/META-INF/plexus/components.xml
deleted file mode 100644
index 915d02a..0000000
--- a/maven-plugin-testing-harness/src/main/resources/META-INF/plexus/components.xml
+++ /dev/null
@@ -1,39 +0,0 @@
-<!--
-  Licensed to the Apache Software Foundation (ASF) under one
-  or more contributor license agreements.  See the NOTICE file
-  distributed with this work for additional information
-  regarding copyright ownership.  The ASF licenses this file
-  to you under the Apache License, Version 2.0 (the
-  "License"); you may not use this file except in compliance
-  with the License.  You may obtain a copy of the License at
-  
-  http://www.apache.org/licenses/LICENSE-2.0
-  
-  Unless required by applicable law or agreed to in writing,
-  software distributed under the License is distributed on an
-  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
-  KIND, either express or implied.  See the License for the
-  specific language governing permissions and limitations
-  under the License.
--->
-
-<component-set>
-  <components>
-    <component>
-      <role>org.codehaus.plexus.component.configurator.expression.ExpressionEvaluator</role>
-      <role-hint>stub-evaluator</role-hint>
-      <implementation>org.apache.maven.plugin.testing.StubResolverExpressionEvaluator</implementation>
-      <requirements>
-        <requirement>
-          <role>org.codehaus.plexus.PlexusContainer</role>
-          <field-name>container</field-name>
-        </requirement>
-      </requirements>
-    </component>
-    <component>
-      <role>org.apache.maven.artifact.Artifact</role>
-      <role-hint>stub</role-hint>
-      <implementation>org.apache.maven.plugin.testing.stubs.StubArtifact</implementation>
-    </component>
-  </components>
-</component-set>
\ No newline at end of file
diff --git a/pom.xml b/pom.xml
index ee20fdf..e2fa417 100644
--- a/pom.xml
+++ b/pom.xml
@@ -101,10 +101,6 @@
     </mailingList>
   </mailingLists>
 
-  <prerequisites>
-    <maven>3.1.1</maven>
-  </prerequisites>
-
   <!-- this project used to be a multimodule project. For easy of history comparison structure is kept -->
   <modules>
     <module>maven-plugin-testing-harness</module>
@@ -134,7 +130,6 @@
   <properties>
     <surefire.version>2.22.2</surefire.version>
     <mavenVersion>3.2.5</mavenVersion>
-    <plexusVersion>1.5.5</plexusVersion>
     <maven.site.path>plugin-testing-archives/LATEST</maven.site.path>
     <javaVersion>7</javaVersion>
     <project.build.outputTimestamp>2020-04-07T21:04:00Z</project.build.outputTimestamp>
@@ -174,17 +169,17 @@
         <version>${mavenVersion}</version>
         <scope>provided</scope>
       </dependency>    
-    
+
       <dependency>
         <groupId>org.codehaus.plexus</groupId>
         <artifactId>plexus-utils</artifactId>
-        <version>3.3.0</version>
+        <version>3.3.0</version> <!-- 3.4.x is Java8 -->
       </dependency>    
     
       <dependency>
         <groupId>junit</groupId>
         <artifactId>junit</artifactId>
-        <version>4.13.1</version>
+        <version>4.13.2</version>
         <scope>provided</scope>
       </dependency>    
     </dependencies>