Remove mean from HPAD pipeline and add tests
Removed commented code
Fix tests
Rename tests for mean() and test both skipna cases
Combine all tests for mean() in one
Fix Test list in docstring for mean() implementation
Fix for complex numbers and comment mean in series_kernels.py
Return mean to series_replace_funcs because it is used in other places
Fix docstring for mean
Return back mean in _run_call_series and add test for default skipna for old style
Improve tests