[515581] Make test plug-ins available from the update-site

Add feature org.eclipse.emf.compare.tests-feature, which contains all
relevant test plug-ins, including their sources.
Also removes an unnecessary plug-in dependency to SysML from uml2.tests.

Change-Id: Ica529319eebd2393fe9d66384b9b771f08a69650
Signed-off-by: Philip Langer <planger@eclipsesource.com>
16 files changed