Remove unused code

It seems that ASP::Processor#process calls #on_if (and not #on_unless)
when encountering an `unless` node.
Remove unused method

This method was left behind after commit 623a886862f15083672057e4fe7a.
Remove unused method
Spec for invalid configuration of Style/Next
Spec for invalid configuration of GuardClause
Spec for invalid config of SpaceInsideBlockBraces
Merge pull request #1535 from bquorning/remove-unused-code

Remove unused code
Merge pull request #1534 from bquorning/spec-invalid-configuration

Spec invalid configuration