Pecl #65615 Remove reserved function names

Certain method names were making it impossible to extend or mock the
built-in Gearman classes.
The following functions/methods have been removed:

- gearman_client_do / GearmanClient::do
- gearman_client_echo / GearmanClient::echo
- gearman_client_clone / GearmanClient::clone
- gearman_worker_echo / GearmanWorker::echo
- gearman_worker_clone / GearmanWorker::clone