Remove unneeded extern crate

bellman/src/gadgets/blake2s.rs

@@ -408,6 +408,7 @@ pub fn blake2s<E: ScalarEngine, CS: ConstraintSystem<E>>(
 #[cfg(test)]
 mod test {
     use blake2s_simd::Params as Blake2sParams;
+    use hex_literal::hex;
     use pairing::bls12_381::Bls12;
     use rand_core::{RngCore, SeedableRng};
     use rand_xorshift::XorShiftRng;

bellman/src/gadgets/sha256.rs

@@ -273,6 +273,7 @@ mod test {
     use super::*;
     use crate::gadgets::boolean::AllocatedBit;
     use crate::gadgets::test::TestConstraintSystem;
+    use hex_literal::hex;
     use pairing::bls12_381::Bls12;
     use rand_core::{RngCore, SeedableRng};
     use rand_xorshift::XorShiftRng;

bellman/src/lib.rs

@@ -135,19 +135,6 @@
 // Catch documentation errors caused by code changes.
 #![deny(intra_doc_link_resolution_failure)]
 
-#[cfg(feature = "multicore")]
-extern crate crossbeam;
-
-#[cfg(feature = "multicore")]
-extern crate num_cpus;
-
-#[cfg(test)]
-#[macro_use]
-extern crate hex_literal;
-
-#[cfg(test)]
-extern crate rand;
-
 pub mod domain;
 pub mod gadgets;
 #[cfg(feature = "groth16")]