Disable the notification subscription.

[dangershony]

This class anyway is not working and waists p2p messages processing

The problem is described in this issue
#434

[dangershony]

The BlockNotification class is a pretty old class that was used to notify light clients of blocks, it seill uses the old signal class.
Since then we have made refactoring to this area of the code, if we find we need to create notifications this has to be completely refactored and maybe use signalr

[dangershony]

This code needs to be double checked in case the notification of transactions was used somehow in other places