Make tests not depend on org.eclipse.ui

de.prob.core.tests/META-INF/MANIFEST.MF

@@ -7,7 +7,6 @@ Bundle-Activator: de.prob.core.tests.Activator
 Require-Bundle: de.prob.core;bundle-version="[9.5.0,9.6.0)",
  org.eclipse.core.resources;bundle-version="[3.13.0,4.0.0)",
  org.eclipse.core.runtime;bundle-version="[3.20.0,4.0.0)",
- org.eclipse.ui;bundle-version="[3.118.0,4.0.0)",
  org.eventb.core;bundle-version="[3.5.0,4.0.0)",
  org.eventb.core.ast;bundle-version="[3.5.0,4.0.0)",
  org.junit;bundle-version="[4.13.0,5.0.0)",

de.prob.core.tests/src/de/prob/core/tests/Activator.java

 package de.prob.core.tests;
 
-import org.eclipse.ui.plugin.AbstractUIPlugin;
+import org.eclipse.core.runtime.Plugin;
 import org.osgi.framework.BundleContext;
 
 /**
  * The activator class controls the plug-in life cycle
  */
-public class Activator extends AbstractUIPlugin {
+public class Activator extends Plugin {
 
 	// The plug-in ID
 	public static final String PLUGIN_ID = "de.prob.core.tests"; //$NON-NLS-1$