Remove stray Signed-off-by in mass rebuild commits
    
    All Fedora contributors must sign FAS to create an account and make
    contributions, so an additional Signed-off-by is not needed. It is
    not used for commits in dist-git.
    
    In fact, having a Signed-off-by is problematic: Signed-off-by by
    itself does not define a meaning, the meaning must be documented
    externally. But Fedora does not provide such a document, so the
    signature is meaningless. And if we were to define such a document in
    the future, it would not cover previous signatures, because we'd have
    no way to know if that's what the signer meant. This would leave to
    massive confusion.
    
    Also, those releng commits are highly visible to all contributors, and
    make it likely the new contributors will copy this.
    
    Drop the siganture to avoid noise and confusion.
    
    Signed-off-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>