Remove unused code in WritableStream
Remove unused code in WritableStream

jmikola/mongo-php-library,jmikola/mongo-php-library,mongodb/mongo-php-library,mongodb/mongo-php-library,jmikola/mongo-php-library,derickr/mongo-php-library,jmikola/mongo-php-library-prototype,10gen-labs/mongo-php-library-prototype,derickr/mongo-php-library,jmikola/mongo-php-library,derickr/mongo-php-library-prototype,mongodb-labs/mongo-php-library-prototype,mongodb/mongo-php-library,mongodb/mongo-php-library