Remove CWalletTx::vfSpent

Use the spent outpoint multimap to figure out which wallet transaction
outputs are unspent, instead of a vfSpent array that is saved
to disk.

src/qt/walletmodel.h

@@ -180,6 +180,7 @@ public:
 
     bool getPubKey(const CKeyID &address, CPubKey& vchPubKeyOut) const;
     void getOutputs(const std::vector<COutPoint>& vOutpoints, std::vector<COutput>& vOutputs);
+    bool isSpent(const COutPoint& outpoint) const;
     void listCoins(std::map<QString, std::vector<COutput> >& mapCoins) const;
 
     bool isLockedCoin(uint256 hash, unsigned int n) const;