Remove unnecessary NONNEGATIVE_SIGNED

Switch to unsigned encoding, which is backwards compatible and avoids MSVC
error reported bitcoin/bitcoin#12732

Author: ryanofsky

src/rpc/blockchain.cpp

@@ -834,7 +834,7 @@ static void ApplyStats(CCoinsStats &stats, CHashWriter& ss, const uint256& hash,
 {
     assert(!outputs.empty());
     ss << hash;
-    ss << VARINT(outputs.begin()->second.nHeight * 2 + outputs.begin()->second.fCoinBase, VarIntMode::NONNEGATIVE_SIGNED);
+    ss << VARINT(outputs.begin()->second.nHeight * 2 + outputs.begin()->second.fCoinBase ? 1u : 0u);
     stats.nTransactions++;
     for (const auto output : outputs) {
         ss << VARINT(output.first + 1);

src/undo.h

@@ -25,7 +25,7 @@ class TxInUndoSerializer
 public:
     template<typename Stream>
     void Serialize(Stream &s) const {
-        ::Serialize(s, VARINT(txout->nHeight * 2 + (txout->fCoinBase ? 1 : 0), VarIntMode::NONNEGATIVE_SIGNED));
+        ::Serialize(s, VARINT(txout->nHeight * 2 + (txout->fCoinBase ? 1u : 0u)));
         if (txout->nHeight > 0) {
             // Required to maintain compatibility with older undo format.
             ::Serialize(s, (unsigned char)0);