rpc: report target height as 0 when synced

since it only makes sense when syncing, and it confuses people

src/rpc/core_rpc_server.cpp

@@ -452,7 +452,7 @@ namespace cryptonote
     m_core.get_blockchain_top(res.height, top_hash);
     ++res.height; // turn top block height into blockchain height
     res.top_block_hash = string_tools::pod_to_hex(top_hash);
-    res.target_height = m_core.get_target_blockchain_height();
+    res.target_height = m_p2p.get_payload_object().is_synchronized() ? 0 : m_core.get_target_blockchain_height();
     store_difficulty(m_core.get_blockchain_storage().get_difficulty_for_next_block(), res.difficulty, res.wide_difficulty, res.difficulty_top64);
     res.target = m_core.get_blockchain_storage().get_difficulty_target();
     res.tx_count = m_core.get_blockchain_storage().get_total_transactions() - res.height; //without coinbase
@@ -2915,7 +2915,7 @@ namespace cryptonote
     crypto::hash top_hash;
     m_core.get_blockchain_top(res.height, top_hash);
     ++res.height; // turn top block height into blockchain height
-    res.target_height = m_core.get_target_blockchain_height();
+    res.target_height = m_p2p.get_payload_object().is_synchronized() ? 0 : m_core.get_target_blockchain_height();
     res.next_needed_pruning_seed = m_p2p.get_payload_object().get_next_needed_pruning_stripe().second;
 
     for (const auto &c: m_p2p.get_payload_object().get_connections())