Remove use of map in early vecs2 exercise

Students do not have the necessary knowledge at this point to understand
what's happening with the iterator combinators. This topic is covered
well by the dedicated exercises about iterators later.

closes #2102

exercises/05_vecs/vecs2.rs

@@ -9,26 +9,6 @@ fn vec_loop(input: &[i32]) -> Vec<i32> {
     output
 }
 
-fn vec_map_example(input: &[i32]) -> Vec<i32> {
-    // An example of collecting a vector after mapping.
-    // We map each element of the `input` slice to its value plus 1.
-    // If the input is `[1, 2, 3]`, the output is `[2, 3, 4]`.
-    input.iter().map(|element| element + 1).collect()
-}
-
-fn vec_map(input: &[i32]) -> Vec<i32> {
-    // TODO: Here, we also want to multiply each element in the `input` slice
-    // by 2, but with iterator mapping instead of manually pushing into an empty
-    // vector.
-    // See the example in the function `vec_map_example` above.
-    input
-        .iter()
-        .map(|element| {
-            // ???
-        })
-        .collect()
-}
-
 fn main() {
     // You can optionally experiment here.
 }
@@ -43,18 +23,4 @@ mod tests {
         let ans = vec_loop(&input);
         assert_eq!(ans, [4, 8, 12, 16, 20]);
     }
-
-    #[test]
-    fn test_vec_map_example() {
-        let input = [1, 2, 3];
-        let ans = vec_map_example(&input);
-        assert_eq!(ans, [2, 3, 4]);
-    }
-
-    #[test]
-    fn test_vec_map() {
-        let input = [2, 4, 6, 8, 10];
-        let ans = vec_map(&input);
-        assert_eq!(ans, [4, 8, 12, 16, 20]);
-    }
 }