Remove warning about parachains and ideal staking rate on Polkadot

[laboon]

https://wiki.polkadot.network/docs/learn-staking-advanced#inflation

We should remove this section (or at least heavily re-word it), since Polkadot ideal staking rate does now change based on the number of parachains and is currently at 45%. There is a bug on the Polkadot-JS UI which still shows it at 75%, however.

THE IDEAL STAKING RATE VARIES BASED ON THE NUMBER OF PARACHAINS
The current staking rate on Polkadot still assumes the absence of parachains, with the suggested ideal staking rate of 75%. You can track the progress on the issue to adjust it here. This code assumes that the number of slots auctioned correspond to the number of parachains on the relaychain, which may not be true as new slots can be occupied by old parachains that are renewing their lease. You can also track the progress on resolving this specific issue here.