Fix unknown additionalparam warning (#455)

This fixes the following warning:

```
[WARNING] Parameter 'additionalparam' is unknown for plugin 'maven-javadoc-plugin:3.4.1:jar (attach-javadocs)'
```

It looks like this was never used ever since it was added in 55a2a1b

Signed-off-by: Wouter Born <github@maindrain.net>

pom.xml

@@ -467,9 +467,6 @@
             <goals>
               <goal>jar</goal>
             </goals>
-            <configuration>
-              <additionalparam>${javadoc.opts}</additionalparam>
-            </configuration>
           </execution>
         </executions>
       </plugin>