Disable enforced coinbase protection in miner_tests.

src/main.h

@@ -116,6 +116,9 @@ extern bool fTxIndex;
 extern bool fIsBareMultisigStd;
 extern bool fCheckBlockIndex;
 extern bool fCheckpointsEnabled;
+// TODO: remove this flag by structuring our code such that
+// it is unneeded for testing
+extern bool fCoinbaseEnforcedProtectionEnabled;
 extern size_t nCoinCacheUsage;
 extern CFeeRate minRelayTxFee;
 extern bool fAlerts;