Remove getBlockDepth method from Chain::interface

Pass conflicting height in CWallet::MarkConflicted

src/interfaces/chain.h

@@ -76,10 +76,6 @@ public:
         //! included in the current chain.
         virtual Optional<int> getBlockHeight(const uint256& hash) = 0;
 
-        //! Get block depth. Returns 1 for chain tip, 2 for preceding block, and
-        //! so on. Returns 0 for a block not included in the current chain.
-        virtual int getBlockDepth(const uint256& hash) = 0;
-
         //! Get block hash. Height must be valid or this function will abort.
         virtual uint256 getBlockHash(int height) = 0;