We also ran into this issue and couldn't find any alternative within Apple's framework; in CFURLAccess.h, Apple recommends using NSURLConnection, but I could not find a way to perform deletions with said class. It would also seem that most third-party libraries make use of CFURLDestroyResource as well.
Then we unearthed this: https://github.com/nkreipke/FTPManager. This FTPManager leverages the fact that Objective-C is a strict superset of C and performs the FTP operations by creating the raw sockets and simply writing the commands manually. It is a method that may be a bit "nuts and bolts" for developers who are accustomed to high-level solutions, but it's elegant in its minimalism and efficiency. And when you get right down to it, most other FTP frameworks are probably executing commands such as these at some level anyway.