Redundant logic in getBlockSlotData

[4miners]

Expected behavior

Logic in modules.delegates->__private.getBlockSlotData should be something like following:

• Call generateDelegatesList.
• Return keypair when delegate for current slot exists in __private.keypairs (forging enabled) or null if not.

Then in __private.forge:

• Remove check described below.
• Remove currentBlockData === null condition form:
  https://github.com/LiskHQ/lisk/blob/7922d346e115406a0004aa729e2ecfd18c5d43e4/modules/delegates.js#L258
• Change check described below to check for currentBlockData === null.
• time can be set directly when calling modules.blocks.process.generateBlock.

Actual behavior

Function modules.delegates->__private.getBlockSlotData is using following logic:

• Call generateDelegatesList.
• Iterate 101 times (through slots) until it finds delegate public key in __private.keypairs.
• Returns slot time together with corresponding keypair or null if it cannot found delegate on the list (forging enabled, but delegate is not the active one).

This function is called form __private.forge in the same module, but later we have a check here:
https://github.com/LiskHQ/lisk/blob/7922d346e115406a0004aa729e2ecfd18c5d43e4/modules/delegates.js#L263-L265 This check is true most of the times because delegate can forge only once during the round (in perfect conditions).

This logic is redundant and unnecessary complex.

Steps to reproduce

N/A

Which version(s) does this affect? (Environment, OS, etc...)

>= 1.0.0