[338] Workaround memory leak in GMF Runtime

Bug: #338
Signed-off-by: Pierre-Charles David <[email protected]>

plugins/org.eclipse.sirius.diagram.ui/src-diag/org/eclipse/sirius/diagram/ui/edit/api/part/AbstractDiagramEdgeEditPart.java

@@ -445,6 +445,7 @@ public void activate() {
     @Override
     public void deactivate() {
         if (isActive()) {
+            removeNotationalListeners();
             DiagramEdgeEditPartOperation.deactivate(this);
             DiagramElementEditPartOperation.deactivate(this);
             super.deactivate();