Fix duplicate word.

Author: LFS6502

library/alloc/src/vec/mod.rs

@@ -3030,8 +3030,8 @@ impl<T: Clone, A: Allocator> Vec<T, A> {
     ///
     /// # Panics if:
     ///
-    /// - Panics if the starting index is greater than the end index.
-    /// - Panics if the end index is greater than the length of the vector.
+    /// - The starting index is greater than the end index.
+    /// - The end index is greater than the length of the vector.
     ///
     /// # Examples
     ///