Mainnet enablement (#2379)

1. Remove the exit guarding running a node in mainnet mode.
2. Set initial difficulty in genesis.

core/src/genesis.rs

@@ -179,7 +179,7 @@ pub fn genesis_main() -> core::Block {
 		output_mmr_size: 1,
 		kernel_mmr_size: 1,
 		pow: ProofOfWork {
-			total_difficulty: Difficulty::from_num(10_u64.pow(8)),
+			total_difficulty: Difficulty::from_num(2_u64.pow(34)),
 			secondary_scaling: 1856,
 			nonce: 1, // REPLACE
 			proof: Proof {

src/bin/grin.rs

@@ -87,12 +87,6 @@ fn real_main() -> i32 {
 		global::ChainTypes::Mainnet
 	};
 
-	// TODO remove for mainnet
-	if chain_type == global::ChainTypes::Mainnet {
-		println!("Mainnet not ready yet! In the meantime run 'grin --floonet ...'");
-		exit(1);
-	}
-
 	// Deal with configuration file creation
 	match args.subcommand() {
 		("server", Some(server_args)) => {