Revert "implement and test Iterator::{exactly_one, collect_array}"

This reverts commit 699184b.

Author: jdonszelmann

library/core/src/iter/traits/iterator.rs

@@ -4034,62 +4034,6 @@ pub trait Iterator {
     {
         unreachable!("Always specialized");
     }
-
-    /// Checks if the iterator contains *exactly* one element.
-    /// If so, returns this one element.
-    ///
-    /// See also [`collect_array`](Iterator::collect_array) for lengths other than `1`.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(exact_length_collection)]
-    ///
-    /// assert_eq!([1].into_iter().exactly_one(), Some(1));
-    /// assert_eq!([].into_iter().exactly_one(), None::<()>);
-    ///
-    /// // There is exactly one even integer in the array:
-    /// assert_eq!([1, 2, 3].into_iter().filter(|x| x % 2 == 0).exactly_one(), Some(2));
-    /// // But there are two odds, which is too many:
-    /// assert_eq!([1, 2, 3].into_iter().filter(|x| x % 2 == 1).exactly_one(), None);
-    /// ```
-    #[inline]
-    #[unstable(feature = "exact_length_collection", issue = "149266")]
-    fn exactly_one(self) -> Option<Self::Item>
-    where
-        Self: Sized,
-    {
-        self.collect_array::<1>().map(|[i]| i)
-    }
-
-    /// Checks if an iterator has *exactly* `N` elements.
-    /// If so, returns those `N` elements in an array.
-    ///
-    /// See also [`exactly_one`](Iterator::exactly_one) when expecting a single element.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(exact_length_collection)]
-    ///
-    /// assert_eq!([1, 2, 3, 4].into_iter().collect_array(), Some([1, 2, 3, 4]));
-    /// assert_eq!([1, 2].into_iter().chain([3, 4]).collect_array(), Some([1, 2, 3, 4]));
-    ///
-    /// // Iterator contains too few elements:
-    /// assert_eq!([1, 2].into_iter().collect_array::<4>(), None);
-    /// // Iterator contains too many elements:
-    /// assert_eq!([1, 2, 3, 4, 5].into_iter().collect_array::<4>(), None);
-    /// // Taking 4 makes it work again:
-    /// assert_eq!([1, 2, 3, 4, 5].into_iter().take(4).collect_array(), Some([1, 2, 3, 4]));
-    /// ```
-    #[inline]
-    #[unstable(feature = "exact_length_collection", issue = "149266")]
-    fn collect_array<const N: usize>(mut self) -> Option<[Self::Item; N]>
-    where
-        Self: Sized,
-    {
-        self.next_chunk().ok().filter(|_| self.next().is_none())
-    }
 }
 
 trait SpecIterEq<B: Iterator>: Iterator {