compressoriterator: avoid redundant cleanup of instance
compressoriterator: avoid redundant cleanup of instance

Py_CLEAR() calls the dealloc() function for the type. This code
is redundant with that function.
terrelln/python-zstandard,indygreg/python-zstandard,indygreg/python-zstandard,indygreg/python-zstandard,terrelln/python-zstandard,terrelln/python-zstandard,terrelln/python-zstandard,indygreg/python-zstandard