[regression] Unnecessary remote repo access for POMs while execution plugin that does not require dependency resolution

Running something simple like "mvn clean" on a project can cause significant performance loss because trunk currently collects the entire dependency tree of the project, i.e. it fetches all dependency POMs (not the JARs) from the configured remote repos. The scope filter that would tell that none of these dependencies is actually required for the current execution is consulted too late.