Fix how upgrades work.

Fix how upgrades work.
Remove some dead code.

src/mem/cache/cache_impl.hh:
    Upgrades don't need a response.
    Moved satisfied check into bus so removed some dead code.
src/mem/cache/coherence/coherence_protocol.cc:
src/mem/packet.hh:
    Upgrades don't require a response

--HG--
extra : convert_revision : dee0440ff19ba4c9e51bf9a47a5b0991265cfc1d