Improvement - Upgrade parent pom

This also requires to upgrade JUnit.
Some test dependencies are already provided by the parent pom and
therefore are not required to be declared explicitly.

pom.xml

@@ -5,8 +5,7 @@
     <parent>
         <groupId>org.jenkins-ci.plugins</groupId>
         <artifactId>plugin</artifactId>
-        <version>2.7</version>
-        <relativePath />
+        <version>3.33</version>
     </parent>
 
     <groupId>org.jenkins.plugins.statistics.gatherer</groupId>
@@ -91,23 +90,10 @@
         </dependency>
 
         <!-- Test dependancies -->
-        <dependency>
-            <groupId>org.jenkins-ci.main</groupId>
-            <artifactId>jenkins-war</artifactId>
-            <version>${jenkins.version}</version>
-            <type>war</type>
-            <scope>test</scope>
-        </dependency>
-        <dependency>
-            <groupId>org.jenkins-ci.main</groupId>
-            <artifactId>jenkins-test-harness</artifactId>
-            <version>${jenkins-test-harness.version}</version>
-            <scope>test</scope>
-        </dependency>
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
-            <version>4.11</version>
+            <version>4.12</version>
             <scope>test</scope>
         </dependency>
         <dependency>