Drop the flow states GK_GRANTED and GK_DECLINED

[AltraMayor]

Once pull request #295 is merged, the flow states GK_GRANTED and GK_DECLINED become redundant since the new flow state GK_BPF can emulate them. Dropping the flow states GK_GRANTED and GK_DECLINED will reduce and simplify the code. If some backward compatibility is needed at the GGU protocol, the dropped states can be easily emulated mapping the old policy decision formats onto their corresponding BPF programs.