Remove unused import (#1758)

Author: ghislainpiot

python-frontend/src/main/java/org/sonar/plugins/python/api/cfg/ControlFlowGraph.java

@@ -28,7 +28,6 @@
 import java.util.Set;
 import java.util.WeakHashMap;
 import java.util.function.Function;
-import java.util.stream.Collectors;
 import javax.annotation.CheckForNull;
 import javax.annotation.Nullable;
 import org.slf4j.Logger;