AtlasPyFwdBwdPorts: fix build warnings (ATLINFR-2605)

Frank Winklmeierrequested to merge
fwinkl/athena:pyfwdbwd_warning into master

Patch two MANIFEST files to not exclude files that have never been included in the first place. This avoids warnings like

warning: no previously-included files matching '*.pyc' found anywhere in distribution

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