dbft: remove useless setters of dBFT interfaces

[AnnaShaleva]

Ref. #84 (comment).

[codecov]

Codecov Report

Attention: Patch coverage is 62.22222% with 17 lines in your changes are missing coverage. Please review.

Project coverage is 63.60%. Comparing base (f3c9fd4) to head (a2fdfa4).

Files	Patch %	Lines
internal/payload/constructors.go	58.06%	13 Missing ⚠️
internal/simulation/main.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #102      +/-   ##
==========================================
- Coverage   63.80%   63.60%   -0.21%     
==========================================
  Files          26       26              
  Lines        1575     1547      -28     
==========================================
- Hits         1005      984      -21     
+ Misses        502      495       -7     
  Partials       68       68              

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[AnnaShaleva]

@roman-khimov, the only question I have is whether we need to remove all these setters from the default payloads implementations? It's kind of internal thing, thus I'm not sure it's worth to refactor it.

UPD: removed, they not needed anymore.

New question: do we need to remove almost all setters and use constructors instead? Like this:

-               commit := c.Config.NewCommit()
-               commit.SetSignature(sign)
+               commit := c.Config.NewCommit(sign)

[roman-khimov]

Like this

Like that. I see no reason for our

s := NewSmth()
s.SetThis()
s.SetThat()

pattern. It's just a bad interface.

[AnnaShaleva]

@roman-khimov, can we keep two setters:

• (Block).SetTransactions([]Transaction[H]), it's needed because block can be constructed prior to all transactions receiving;
• (ConsensusPayload).SetValidatorIndex, it's needed to avoid passing the same argument to all constructors. For code shortness.

[roman-khimov]

can we keep two setters

Sure, if they're justified. SetTransactions() is special, OK. SetValidatorIndex() seems to be required for recoveries.