Erase the leaving symbols, not the entering symbols in dualOptimize. Matches the Kiwi C++ implementation: 0989ff015f/kiwi/solverimpl.h (L615)

src/main/java/no/birkett/kiwi/Solver.java

@@ -530,7 +530,7 @@ public class Solver {
                 if(entering.getType() == Symbol.Type.INVALID){
                     throw new InternalSolverError("internal solver error");
                 }
-                rows.remove(entering);
+                rows.remove(leaving);
                 row.solveFor(leaving, entering);
                 substitute(entering, row);
                 rows.put(entering, row);