ARTEMIS-6145 Remove unused activemq-stomp dependency

The activemq-stomp artifact is declared as a dependency in
activemq5-unit-tests but no code in the module imports or uses any
class from it. Removing it to keep the dependency tree clean.

Author: lavocatt

tests/activemq5-unit-tests/pom.xml

@@ -85,12 +85,6 @@
          <version>${activemq5-version}</version>
       </dependency>
 
-      <dependency>
-         <groupId>org.apache.activemq</groupId>
-         <artifactId>activemq-stomp</artifactId>
-         <version>${activemq5-version}</version>
-      </dependency>
-
       <dependency>
          <groupId>junit</groupId>
          <artifactId>junit</artifactId>