Minor simplification of SymbolTable::addDiffAuxiliaryVar()

For symmetry with SymbolTable::addUnaryOpAuxiliaryVar().

src/SymbolTable.cc

@@ -594,12 +594,6 @@ SymbolTable::addDiffAuxiliaryVar(int index, expr_t expr_arg, int orig_symb_id, i
   return symb_id;
 }
 
-int
-SymbolTable::addDiffAuxiliaryVar(int index, expr_t expr_arg) noexcept(false)
-{
-  return addDiffAuxiliaryVar(index, expr_arg, -1, 0);
-}
-
 int
 SymbolTable::addUnaryOpAuxiliaryVar(int index, expr_t expr_arg, string unary_op, int orig_symb_id, int orig_lag) noexcept(false)
 {

src/SymbolTable.hh

@@ -343,8 +343,7 @@ public:
      diffLead increases it). */
   pair<int, int> unrollDiffLeadLagChain(int symb_id, int lag) const noexcept(false);
   //! Adds an auxiliary variable when the diff operator is encountered
-  int addDiffAuxiliaryVar(int index, expr_t expr_arg) noexcept(false);
-  int addDiffAuxiliaryVar(int index, expr_t expr_arg, int orig_symb_id, int orig_lag) noexcept(false);
+  int addDiffAuxiliaryVar(int index, expr_t expr_arg, int orig_symb_id = -1, int orig_lag = 0) noexcept(false);
   //! Takes care of timing between diff statements
   int addDiffLagAuxiliaryVar(int index, expr_t expr_arg, int orig_symb_id, int orig_lag) noexcept(false);
   //! Takes care of timing between diff statements