Autoload destroy without sub

Remove inline tests from PPI::Statement.

Resolution of issue #31: RT 27364: DESTROY and AUTOLOAD don't parse as subs without 'sub'. DESTROY and AUTOLOAD without a preceding 'sub' now parse as PPI::Statement::Sub, which is what they're currently parsed as when 'sub' is present.

Create separate test files t/ppi_statement_sub.t and t/ppi_statement_scheduled.t.