Low: libcrmcommon: handle disconnected attrd API connections consistently

Drop send_attrd_request() in favor of using connect_and_send_attrd_request(),
since pcmk__connect_ipc() will return pcmk_rc_ok immediately if the API is
already connected.

All the attribute manager IPC APIs attempted the connection if not already
connected except for pcmk__attrd_api_query(). Now that it uses
connect_and_send_attrd_request(), they are all consistent.