config: default acceptnonstdtxn=0 on all chains

Previously, the default for acceptnonstdtxn defaulted to 0 on all
chains except testnet. Change this to be consistent across all
chains, and remove the parameter from chainparams entirely.

src/kernel/chainparams.h

@@ -102,8 +102,6 @@ public:
     const CBlock& GenesisBlock() const { return genesis; }
     /** Default value for -checkmempool and -checkblockindex argument */
     bool DefaultConsistencyChecks() const { return fDefaultConsistencyChecks; }
-    /** Policy: Filter transactions that do not match well-defined patterns */
-    bool RequireStandard() const { return fRequireStandard; }
     /** If this chain is exclusively used for testing */
     bool IsTestChain() const { return m_is_test_chain; }
     /** If this chain allows time to be mocked */
@@ -179,7 +177,6 @@ protected:
     CBlock genesis;
     std::vector<uint8_t> vFixedSeeds;
     bool fDefaultConsistencyChecks;
-    bool fRequireStandard;
     bool m_is_test_chain;
     bool m_is_mockable_chain;
     CCheckpointData checkpointData;