Get rid of "dead" ledgers. We don't need them any more and they make trouble.

Fix close time synch to be more accurate.

src/ValidationCollection.h

@@ -20,7 +20,6 @@ protected:
 	boost::unordered_map<uint256, ValidationSet> 					mValidations;
 	boost::unordered_map<uint160, SerializedValidation::pointer> 	mCurrentValidations;
 	std::vector<SerializedValidation::pointer> 						mStaleValidations;
-	std::list<uint256>												mDeadLedgers;
 
 	bool mWriting;
 
@@ -39,10 +38,6 @@ public:
 
 	boost::unordered_map<uint256, int> getCurrentValidations(uint256 currentLedger = uint256());
 
-	void addDeadLedger(const uint256&);
-	bool isDeadLedger(const uint256&);
-	std::list<uint256> getDeadLedgers() { return mDeadLedgers; }
-
 	void flush();
 };