Fix for BrickFTP (#1489736), spec clean-up
    
    - scp: Do not NUL-terminate the command for remote exec (#1489736, GH#208)
    - Make devel package dependency on main package arch-specific
    - Drop EL-5 support
      - noarch sub-packages always available now
      - Drop legacy Group: and BuildRoot: tags
      - Drop explicit buildroot cleaning
      - %{__isa_bits} always defined now