Stop packaging cows in the unsupported *.pm format
    
    The cowsay code does not support cows in the *.pm format.
    
    As "cowsay -r" occasionally selects one unsupported *.pm
    format cow purely by chance, "cowsay -r" will produce an
    error message instead of a cow in these occasions.
    
    Not packaging the *.pm cows avoids the issue until upstream
    either stops considering unsupported cows for random
    selection or implements support for *.pm format cows.
    
    The upstream bug is https://github.com/cowsay-org/cowsay/issues/22
    and affects at least cowsay-3.7.0. It is currently marked
    to be resolved in cowsay-3.8.0 (the random selection part,
    not the *.pm implementation part).