Remove unused $notify in check.pp

Currenlty its not possible to run the sensu puppet module with
puppet 3.6 because of a redelcaration of $notify in check.pp
This var was introduced with 62d7c948ca3ad8c16ab8aa5939dbaa69584f9f82
but is obsolete since a296283c193b166859d7390a23960346f6c12aa9 because
of the renaming.