Remove unnecessary import from doctests

Author: djc

library/alloc/src/vec/mod.rs

@@ -2696,22 +2696,19 @@ impl<T, A: Allocator, const N: usize> TryFrom<Vec<T, A>> for [T; N] {
     /// # Examples
     ///
     /// ```
-    /// use std::convert::TryInto;
     /// assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
     /// assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
     /// ```
     ///
     /// If the length doesn't match, the input comes back in `Err`:
     /// ```
-    /// use std::convert::TryInto;
     /// let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
     /// assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
     /// ```
     ///
     /// If you're fine with just getting a prefix of the `Vec<T>`,
     /// you can call [`.truncate(N)`](Vec::truncate) first.
     /// ```
-    /// use std::convert::TryInto;
     /// let mut v = String::from("hello world").into_bytes();
     /// v.sort();
     /// v.truncate(2);