Remove unecessary check in pipe.rs (#1763)

chain/src/pipe.rs

@@ -28,7 +28,7 @@ use core::core::verifier_cache::VerifierCache;
 use core::core::Committed;
 use core::core::{Block, BlockHeader, BlockSums};
 use core::global;
-use core::pow::{self, Difficulty};
+use core::pow;
 use error::{Error, ErrorKind};
 use grin_store;
 use store;
@@ -424,12 +424,6 @@ fn validate_header(header: &BlockHeader, ctx: &mut BlockContext) -> Result<(), E
 			return Err(ErrorKind::DifficultyTooLow.into());
 		}
 
-		// explicit check to ensure we are not below the minimum difficulty
-		// we will also check difficulty based on next_difficulty later on
-		if target_difficulty < Difficulty::one() {
-			return Err(ErrorKind::DifficultyTooLow.into());
-		}
-
 		// explicit check to ensure total_difficulty has increased by exactly
 		// the _network_ difficulty of the previous block
 		// (during testnet1 we use _block_ difficulty here)