get_config_info function in 'ExternalBotHandler' class was
using 2 undefined variables, which wasn't allowing bots to
access information from config file.
Fixed it, bots with api key working now.
Previously, the annotation for the (now removed)send-reply
function was also wrong, as "send-message" function of
EmbeddedBotHandler class does not return any value, contrary
to "Dict[str, Any]" as specified by the funtion.
This is done as a follow up for zulip/zulip#5842.
