function DestroyableTransform(opts) {
  Transform.call(this, opts)
  this._destroyed = false
}
Compiles schema to validation function
@this   Ajv
@param  {Object} schema schema object
@param  {Object} root object with information about the root schema for this schema
@param  {Object} localRefs the hash of local references inside the schema (created by resolve.id), used for inline resolution
@param  {String} baseId base ID for IDs in the schema
@return {Function} validation function