reset ast trail on context deletion

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

src/api/api_context.cpp

@@ -128,6 +128,7 @@ namespace api {
             for (unsigned i = 0; i < m_replay_stack.size(); ++i) {
                 dealloc(m_replay_stack[i]);
             }
+            m_ast_trail.reset();
         }
         reset_parser();
         dealloc(m_solver);