cql3: remove a dynamic_pointer_cast to user_type_impl.
cql3: remove a dynamic_pointer_cast to user_type_impl.

There exists a method to check if something is a user type:
is_user_type(); use it instead.

scylladb/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla