Remove unparsing for guarding

* With the monkeypatch to parser it this is not needed anymore.
* Mutant will NOT be released with this monkeypatch, I'll try to get it
  upstream soon.
* Performance for the mutation corpus test is greatly improved.
* Positive performance chance for regular mutant runs is visible.
Adjust self coverage configurations
Remove guard via identity

* Simplify spec helper via mutation verifier class
* There was no need to guard via mapped identity anymore.
Emit random names as symbolx
Use unparser CLI api correctly
Normalize nodes before unparser test
Bump unparser dependency