removed assertion from Simplex.cpp as per review

Author: xgupta

mlir/lib/Analysis/Presburger/Simplex.cpp

@@ -106,7 +106,6 @@ Simplex::Unknown &SimplexBase::unknownFromRow(unsigned row) {
 
 unsigned SimplexBase::addZeroRow(bool makeRestricted) {
   // Resize the tableau to accommodate the extra row.
-  unsigned oldNumRows = getNumRows();
   unsigned newRow = tableau.appendExtraRow();
   rowUnknown.emplace_back(~con.size());
   con.emplace_back(Orientation::Row, makeRestricted, newRow);