Rm content related to Im-Online Pallet

[filippoweb3]

• Unresponsiveness
• im-online session keys

[filippoweb3]

@Overkillus, can you please check if I removed the right content? Essentially, I removed im-online pallet-related stuff (slashing for unresponsiveness, heartbeat content, and online messages).

[Overkillus]

Added some relatively important nits but overall looking nice. Check here for a more comprehensive list of changes: https://github.com/orgs/paritytech/projects/119/views/15?pane=issue&itemId=61684472

I will also do one more scan of the whole staking section of the wiki to check if we didn't miss anything.

[Overkillus]

Did a quick scan and found some stale mentions:

• :::warning Single Operators with Multiple Validators as it mentions ImOnline within Learn -> Nominator
• The removal of a percentage of an account's DOT as a punishment for a validator acting maliciously or incompetently (e.g., equivocating or remaining offline for an extended period). in Glossary -> Slashing
• #### Commission Fees & Slashes The network slashes a validator for a misbehavior (e.g. validator offline, equivocation, etc.) -> mentions offline slashes
• and equivocation offenses are slashed at much higher rates than equivalent offline offenses.
• Slashing will happen if a validator misbehaves (e.g. goes offline, attacks the network, or runs modified software)
• Validators perform critical functions for the network, and as such, have strict uptime requirements. [...] -> mentions getting ImOnline slashed a bit further
• Remember, even if your validator goes offline for some time, the offline slash is much more forgiving than the equivocation or parachain validity slashing.
• Slashing penalties for being offline are much less than those for equivocation.

Please re-check if you missed some others if possible. I searched for offline, online keywords but hopefully those are all the mentions.

Not connected to disabling but I spotted it:

• The minimal safe ratio of validators per parachain is 5:1. With a sufficiently large set of validators, the randomness of their distribution along with -> we currently use 3:1 in Kusama and we believe it is safe.

[DrW3RK]

Looks good to me.