mist_cleanup.js

//Remove contracts by ID
CustomContracts.find().fetch();
CustomContracts.remove("_CONTRACT_ID_");

//Remove tokens by ID
Tokens.find().fetch();
Tokens.remove("_TOKEN_ID_");

//Remove all contracts
CustomContracts.find().fetch().map(
   function(m) { CustomContracts.remove(m._id);}
);

//remove only with condition
CustomContracts.find().fetch().map(
   function(m) { if (m.name == '-') {CustomContracts.remove(m._id);}}
);