[cleanup] Remove unused import

Change-Id: I75d2decef319682b000f3c82dec1de2eaa1c4a89
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>
diff --git a/plugins/org.eclipse.sirius.ext.base/src/org/eclipse/sirius/ext/base/relations/TransitiveClosure.java b/plugins/org.eclipse.sirius.ext.base/src/org/eclipse/sirius/ext/base/relations/TransitiveClosure.java
index 102fa22..2d7614e 100644
--- a/plugins/org.eclipse.sirius.ext.base/src/org/eclipse/sirius/ext/base/relations/TransitiveClosure.java
+++ b/plugins/org.eclipse.sirius.ext.base/src/org/eclipse/sirius/ext/base/relations/TransitiveClosure.java
@@ -18,7 +18,6 @@
 
 import org.eclipse.sirius.ext.base.Messages;
 
-import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableSet;
 
 /**