Remove outdated dependency junit-addons

[stefanseifert]

Description

remove this dependency from parent POM and core module:

            <dependency>
                <groupId>junit-addons</groupId>
                <artifactId>junit-addons</artifactId>
                <version>1.4</version>
                <scope>test</scope>
            </dependency>

Related Issue

Fixes #920

Motivation and Context

this dependency is completely outdated (more than 20 years old!!), it's not compatible/usable with JUnit 5+, and even worse, it breaks JSON content loading when using AEM mocks, as it injects an outdated Xerces version into the test build classpath (as described in #920). it should be removed without replacement.

How Has This Been Tested?

the archetype build including its ITs is passing without this dependency.