Fix `capture' memory management

The capture action was implemented before the transaction concept.
While partially ported to use the transaction, some of the elements
were not freed correctly. Now it is fully ported to use the class
Transaction.

src/operators/pm.h

@@ -42,7 +42,6 @@ class Pm : public Operator {
     bool init(const std::string &file, const char **error) override;
     void postOrderTraversal(acmp_btree_node_t *node);
 
-    std::list<std::string> matched;
  protected:
     ACMP *m_p;
 };