Remove now redundant import

Author: Joel Allred

jbmc/unit/solvers/strings/string_refinement/dependency_graph.cpp

@@ -11,7 +11,6 @@ Author: Diffblue Ltd.
 
 #include <java_bytecode/java_types.h>
 #include <solvers/strings/string_dependencies.h>
-#include <solvers/strings/string_refinement_util.h>
 #include <util/arith_tools.h>
 #include <util/std_expr.h>
 #include <util/std_types.h>