Remove unused imports.

src/bigint.rs

@@ -1421,7 +1421,7 @@ impl BigInt {
 #[cfg(test)]
 mod biguint_tests {
     use Integer;
-    use super::{BigDigit, BigUint, ToBigUint, to_str_radix, to_str_radix_signed};
+    use super::{BigDigit, BigUint, ToBigUint, to_str_radix};
     use super::{Plus, BigInt, RandBigInt, ToBigInt};
 
     use std::cmp::{Less, Equal, Greater};

src/rational.rs

@@ -386,7 +386,7 @@ impl<T: FromStrRadix + Clone + Integer + PartialOrd>
 mod test {
 
     use super::{Ratio, Rational, BigRational};
-    use std::num::{Zero, One, FromStrRadix, FromPrimitive};
+    use std::num::{Zero, One, FromPrimitive};
     use std::from_str::FromStr;
     use std::hash::hash;
     use std::num;