remove ref to theory_str

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/smt/smt_theory.h

@@ -283,7 +283,6 @@ namespace smt {
         /**
            \brief This method is called by smt_context before the search starts
            to get any extra assumptions the theory wants to use.
-           (See theory_str for an example)
         */
         virtual void add_theory_assumptions(expr_ref_vector & assumptions) {
         }