multi: Keep itest default miner as btcd

Do not change the miner backend implicitly when running with a bitcoind
chain backend. The bitcoind-backed miner should be opt-in via the
-minerbackend flag.

Author: bhandras

itest/default_miner_backend_bitcoind.go

@@ -89,8 +89,7 @@ var (
 	)
 
 	// minerBackendFlag selects which miner backend to use. If not set, a
-	// default is chosen based on build tags (e.g. `backend=bitcoind` will
-	// default to a bitcoind miner).
+	// default miner is used.
 	minerBackendFlag = flag.String(
 		"minerbackend", "", "miner backend (btcd, bitcoind)",
 	)
@@ -112,13 +111,11 @@ func TestLightningNetworkDaemon(t *testing.T) {
 
 	// Get the binary path and setup the harness test.
 	binary := getLndBinary(t)
-	minerBackend := defaultMinerBackend
+	var minerCfg *miner.MinerConfig
 	if minerBackendFlag != nil && *minerBackendFlag != "" {
-		minerBackend = *minerBackendFlag
-	}
-
-	minerCfg := &miner.MinerConfig{
-		Backend: minerBackend,
+		minerCfg = &miner.MinerConfig{
+			Backend: *minerBackendFlag,
+		}
 	}
 
 	harnessTest := lntest.SetupHarnessWithMinerConfig(