lib/sync-server.js
function removeCollision(datasetId, params, cb) {
  debug('[%s] removeCollision');
  dataHandlers.removeCollision(datasetId, params.hash, params.meta_data, cb);
}
function removeCollision(datasetId, params, cb) {
  debug('[%s] removeCollision');
  dataHandlers.removeCollision(datasetId, params.hash, params.meta_data, cb);
}
Defines a handler function for deleting a collision from the collisions list.
Should be called after the dataset is initialised.