562892c [Trivial] Rename MintableCoins() --> StakeableCoins() (random-zebra)
7431f09 [Wallet][Cleanup] Remove SelectStakeCoins (random-zebra)
33c3973 [Wallet] Faster lookup for MintableCoins (random-zebra)
bc6ae73 [Wallet] Check min depth requirement for stake inputs in AvailableCoins (random-zebra)
016a60e [Wallet][RPC] Remove GetStakingBalance calls to get staking status (random-zebra)
cf5f2d2 [Cleanup][Wallet] Don't count zPIV in MintableCoins() (random-zebra)

Pull request description:

  - 1st commit removes zPIV balance count in `CWallet::MintableCoins()` (as mints cannot stake anymore).

  - 2nd commit removes `GetStakingBalance` calls in BitcoinMiner and `getstakingstatus` RPC (thus removing "enoughcoins", leaving only "mintablecoins" field there).
  `MintableCoins()` already checks the staking balance and returns false if it is either non-positive or less than the reserve balance.

  - 3rd commit removes the depth requirement check from `MintableCoins`, moving it directly in `AvailableCoins` (no need to check for age anymore, only depth).

  - 4th commit introduces a performance improvement (which might be significative on wallets with many utxos). Since the only purpose of `MintableCoins` is to verify that there is *at least one* eligible utxo, there is no need to get the whole set of them from `AvailableCoins`.
  And since this function is checked often when staking (`AvailableCoins` is called again from within `CreateCoinStake`) it's better to introduce a way to outright return from it, as soon as a valid utxo is found. This commit also removes the extra `LOCK(cs_main)` in the function.

  - 5th commit reworks MintableCoins/AvailableCoins/CreateCoinStake to remove `SelectStakeCoins` and avoid duplicated code in yet another place.

  - 6th commit finally renames `MintableCoins` --> `StakeableCoins` to avoid possible confusion.

ACKs for top commit:
  Fuzzbawls:
    ACK 562892c
  furszy:
    ACK 562892c

Tree-SHA512: 80878f09973e841ac13da46766a08191d066f6298d0ef9d55a6ecfa9013125f73f85f61d8e0b469c5b7373a764e72e5187406fdea54ca1eaff84d762ae337146

7a8d755 [Tests] Remove '-staking' from extra-args (random-zebra)
72d5a31 [Tests] Fix/Update mining_pos_coldstaking test (random-zebra)
5ffa6b5 [Trivial] Rename mintablecoins --> stakeablecoins (random-zebra)
e781cd0 [Cleanup] zPIV Don't validate Accumulator Checkpoints anymore (random-zebra)
5b192e0 [Tests][Bug] Fix staking status in generate_pos() (random-zebra)

Pull request description:

  This is based on top of #1276 and #1277 which should be reviewed before.
  `generate_pos` framework function relies on the output of `getstakingstatus` RPC which was recently changed.
  Since #1245, "validtime" is not returned anymore (nor it was ever really needed here).
  Only things that we need in `generate_pos` are "walletunlocked" and "mintablecoins" (renamed "stakeablecoins").
  "enoughcoins" is going to be removed in #1277 , and "haveconnections" is not required on regtest.
  This also updates coldstaking test.

ACKs for top commit:
  Fuzzbawls:
    ACK 7a8d755
  furszy:
    ACK 7a8d755

Tree-SHA512: 0f45d8b3880d8d88258861fc85c04e0c62a834cede8991e1370afcaef05a2fb714a4441e201d0bdfd89251628e92aa51496182b8088917a8f3a9b740a21272f6

799e3ad [Tests] Fix block version on RegTest (random-zebra)
00aae54 [Core][Cleanup] PoS: remove extra signature + IncrementExtraNonce (random-zebra)
389094f [Core] Remove StakeV1 in kernel and miner (random-zebra)

Pull request description:

  This removes the old StakeV1 function and does some minor optimizations in the miner code (removing redundant signature and IncrementExtraNonce calls).

  This is based on top of the following three pull requests and will be rebased after their merge into master.
  So, they should be reviewed before this one.
  - [x] #1276
  - [x] #1277
  - [x] #1278

ACKs for top commit:
  furszy:
    Staking working properly, ACK 799e3ad
  Fuzzbawls:
    ACK 799e3ad

Tree-SHA512: a3cde86fc3a7cdad39d8d322dbcc0da1e34d044c4f320700605a9952e67788c825b53516e5ff452e37cde127aaf902416168dc6384fe62954d336efe7aea23eb