(server-clients): Only keep procs, no properties any more.

(server-clients): Only keep procs, no properties any more.
(server-client): Remove.
(server-client-get, server-client-set): Remove, replace all callers by
process-get and process-put resp.
(server-clients-with, server-add-client, server-delete-client)
(server-create-tty-frame, server-create-window-system-frame)
(server-process-filter, server-execute, server-visit-files)
(server-buffer-done, server-kill-buffer-query-function)
(server-kill-emacs-query-function, server-switch-buffer)
(server-save-buffers-kill-terminal): Update accordingly.