cam-service: Remove unused parameter from service config

The connection parameter in cam_service_cfg can not be modified via
command line, and we can always access CONFIG_CAM_SERVICE_MAX_CONN
to get the maximum support connections, so remove this parameter
from cam_service_cfg.

Same reason for removing it from cam_socket_cfg struct.

Signed-off-by: Hongda Deng <hongda.deng@arm.com>