fix gc to not remove ternary clauses that are on assignment trail. This addresses issue with drat proofs that don't pass drat-trim due to deletion during gc, but use in conflicts

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

src/sat/tactic/sat_tactic.cpp

@@ -200,6 +200,7 @@ public:
             throw tactic_exception(ex.msg());
         }
         catch (z3_exception& ex) {
+            (void)ex;
             TRACE("sat", tout << ex.msg() << "\n";);            
             throw;
         }