Remove zeroed sockets_used/sockets_total

[lhoguin]

Values are zeroed following 4.x changes.

FYI I am not a .NET developer so not sure if I broke something.
I just work on rabbit.

There are other values that have been zeroed in recent years,
including many values in [1] that I may send PRs for at a later
time.

[1] https://github.com/EasyNetQ/EasyNetQ.Management.Client/blob/master/Source/EasyNetQ.Management.Client/Model/BackingQueueStatus.cs

[inikulshin]

@lhoguin EasyNetQ.Management.Client supports RabbitMQ back to 3.10.

I don't know if there is any rule or commitment about that (@Pliner @zidad, but it's one of the most important things to be written in README), but at least we run tests on 3.10, 3.11, 3.12 and 3.13.

Is it ok to make your changes for all those RabbitMQ versions?

[lhoguin]

The variables that are removed in this PR can be obtained with better accuracy from system metrics. They are also not very useful but it's possible that someone relies on them.

There's no urgency in merging this, the values will just be 0 for 4.x onward.

[michaelklishin]

@inikulshin dropping these metrics should not break anything even for 3.10 (that has been out of any kind of support from the RabbitMQ Team since Dec 2023), unless the JSON parser/mapper used explicitly requires all keys in a JSON document to be mapped. Which is usually not the case.

These metrics are kernel ones and should not be monitored by RabbitMQ itself, hence they were removed from RabbitMQ itself. All that means is that certain API responses now have two fewer JSON object keys.

[michaelklishin]

FTR, the two metrics were removed in rabbitmq/rabbitmq-server#11436.

[inikulshin]

@michaelklishin I'm 99.9% sure nobody ever used those metrics. :)

But my question is if they were set in response JSON in any of currently supported RabbitMQ versions?

[michaelklishin]

They are still returned by 3.13.x and all the series you mention above.