Rename nullifier caches and maps to indicate sprout nullifiers

src/zcbenchmarks.cpp

@@ -382,7 +382,7 @@ public:
                     const uint256 &hashBlock,
                     const uint256 &hashAnchor,
                     CAnchorsMap &mapAnchors,
-                    CNullifiersMap &mapNullifiers,
+                    CNullifiersMap &mapSproutNullifiers,
                     CNullifiersMap& mapSaplingNullifiers) {
         return false;
     }