Revert elixir json switch

[mkuratczyk]

Unfortunately the switch to rabbit_json/thoas led to some commands failing:

> rabbitmqctl list_stream_connections --formatter json conn_name
[
{"conn_name":"127.0.0.1:60556 -> 127.0.0.1:5552"}
,{"conn_name":"127.0.0.1:60552 -> 127.0.0.1:5552"}
,{"conn_name":"127.0.0.1:60555 -> 127.0.0.1:5552"}
]

> rabbitmqctl list_stream_connections --formatter json conn_name,client_properties
[
{:badmatch, {:error, :function_clause}}

We'll look into this at some point. For now, let's revert.

References #9926 #9932.