Remove unused default args to Invalid and DoS

[Empact]

These unused default args increase risk related to pending
refactoring of these interfaces.

[Empact]

After taking a few passes at this refactoring, I realized I want to keep the existing names if possible, so this is a step toward reducing risk associated with that, see:
#12976 (comment)
#12463 (comment)

[practicalswift]

Concept ACK

[jnewbery]

Rather than these minor refactors, I'd much rather see progress made on #11639, which clarifies the interface between net_processing and validation. It'd be a shame to have to rebase that PR and waste the reviewer cycles there.

@Empact - how would you feel about reviewing that PR?

[Empact]

@jnewbery Sorry, I'm at stage where I see the codebase more in the small than in the large, and I take the smaller PRs as neatly packaged unambiguous improvements. This was setting us up for this simplification: https://github.com/bitcoin/bitcoin/compare/master...Empact:drop-dos-return-corruption-scripted?expand=1

As for #11639, I like it, I'll make some comments over there. IMO its a bit easier to reason about after applying my changes:
https://github.com/bitcoin/bitcoin/compare/master...Empact:2017-10-dos-rewrite?expand=1

[Empact]

@jnewbery thanks for the guidance, will reopen post-#11639