Doc: Improved documentation on (in)active arguments in `delegates` RPC

Context

Closes #2172 (closed)

When using the RPC call /context/delegates the use of arguments "active"/"inactive" isn't most intuitive, in that when setting active = false or inactive = false (or both), all delegates are still returned. Essentially the arguments only work in the affirmative, i.e. setting them to false has no effect.

So, we added text in the RPC documentation simply stating "setting these arguments to false has no effect."

Manually testing the MR

This html files changed: tezos/docs/_build/alpha/rpc.html

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