zlib.compress can now only be used to output zlib blocks.
Arguably `zlib.compress(my_data, level, wbits=-15)` is even more useful as it gives you a raw deflate block. That is quite interesting if you are writing your own file format and want to use compression, but like to use a different hash.

Also gzip.compress(data, level, mtime) is extremely slow due to it instantiating a GzipFile object which then streams a bytes object. Explicitly not taking advantage of the fact that the bytes object is entirely in memory already (I will create another bug for this). zlib.compress(my_data, level, wbits=31) should be faster in all possible circumstances, but that option is not available now.