multi: Remove deprecated missed and expired tickets RPCs.

[davecgh]

This requires #2909 and #2910.

Per the second phase of #2774, this removes all RPCs and associated code related to missed and expired tickets.

As stated in the original proposal, the only known way these RPCs are used is to support wallet staking statistics, but due to the automatic revocations consensus change, wallets will not really need the RPCs to calculate the vast majority of the information anymore since they can detect missed and expired tickets through a combination of seeing the revocation and comparing the number of confirmations against the ticket purchase height.

Further, these RPCs are really not something that dcrd should be maintaining by default anyway because they have some fairly significant downsides:

• The set of missed tickets and revoked tickets are both unbounded which means they take up more and more resources over time
• With the automatic revocations consensus change, the entire notion of a missed category effectively no longer exists
• The sets are already large enough that they take a non-trivial amount of RAM and I/O and will only become more burdensome over time
• Even though the missed category will effectively no longer exist, continued support of these RPCs requires the current ticket database and related consensus code to continue to be able to track and manipulate these unbounded sets

That final point is perhaps one of the most important ones, because the ticket database design can be significantly optimized due to the introduction of the automatic revocations consensus change so long as the RPCs in question are no longer supported.

The removals have been split into multiple commits to ease the review process and also ensure everything continues to work properly each step of the way.

The following is a high level overview of the changes:

• Bumps the RPC server major version to 8.0.0
• Removes the entries for the following RPCs and notifications from the JSON-RPC API docs:
  • missedtickets
  • rebroadcastmissed
  • existsmissedtickets
  • existsexpiredtickets
  • notifyspentandmissedtickets
  • spentandmissedtickets
• Removes all code for the following methods and notification tracking from the rpcclient:
  • MissedTicketsAsync
  • MissedTickets
  • ExistsMissedTicketsAsync
  • ExistsMissedTickets
  • ExistsExpiredTicketsAsync
  • ExistsExpiredTickets
  • NotifySpentAndMissedTicketsAsync
  • NotifySpentAndMissedTickets
  • OnSpentAndMissedTickets
• Removes all code from the RPC server for handling the following RPCs and notifications:
  • missedtickets
  • rebroadcastmissed
  • existsmissedtickets
  • existsexpiredtickets
  • notifyspentandmissedtickets
  • spentandmissedtickets
• Removes the following methods from blockchain that are no longer used as they only existed to support the RPCs:
  • MissedTickets
  • CheckMissedTickets
  • CheckExpiredTicket
  • CheckExpiredTickets
• Removes the NTSpentAndMissedTickets and associated code to send the notification from blockchain
• Updates the blockchain.TicketNotificationsData struct to remove the TicketsSpent and TicketsMissed fields
• Removes the following types, constants, and registrations along with associated tests from rpc/jsonrpc/types:
  • MissedTicketsCmd
  • MissedTicketsResult
  • RebroadcastMissedCmd
  • ExistsMissedTicketsCmd
  • ExistsExpiredTicketsCmd
  • NotifySpentAndMissedTicketsCmd
  • SpentAndMissedTicketsNtfnMethod
  • SpentAndMissedTicketsNtfn

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This closes #2774.

[davecgh]

As an additional point, I debated whether or not to replace the notifyspentandmissedtickets with a notifyspenttickets notification, but I decided against it because it would contain the exact same information as notifywinningtickets given every block after the autorevocations consensus change is active will necessarily spend all of the winning tickets through a vote or an automatic revocation.

[rstaudt2]

Looks good, nice to see all of that removed. All of the separate commits made this really easy to follow.