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.
Test EmptyLinesAroundClassBody on singleton class
Spec for Token#to_s

Token#to_s was introduced in https://github.com/bbatsov/rubocop/pull/8
and seems untested forever. I assume it was introduced for debugging
purposes.
Test RedundantSelf with class methods, too
Spec for invalid configuration of Style/Next
Spec for invalid configuration of GuardClause
Spec for missing configuration of GlobalVars
Test LiteralInCondition on post-loop while/until
Spec deprecation of -e and -s options flags
Remove specs for RuboCop v1.0.0