Omit __pycache__ directories from wheels

[stefan6419846]

At the moment, the wheel on PyPI ships with all __pycache__ directories, which does not make much sense. Example:

suds/__pycache__/__init__.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/builder.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/cache.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/client.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/compat.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/metrics.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/options.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/plugin.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/properties.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/reader.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/resolver.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/servicedefinition.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/serviceproxy.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/soaparray.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/store.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/sudsobject.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/utils.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/wsdl.cpython-38.opt-1.pyc                                                                        
suds/__pycache__/wsse.cpython-38.opt-1.pyc    

If ever, these files will only be useful on Python 3.8, and thus only bloat the distributions.