fix(curriculum): Consolidated comments for JavaScript Algorithms and Data Structures challenges - part 1 of 4 (#38258)

* fix: consolidate/remove comments

* fix: remove => from comment

* fix: reverted changes to add same changes to another PR

* fix: removed 'the' from sentence

Co-Authored-By: Oliver Eyton-Williams <ojeytonwilliams@gmail.com>

* fix: removed 'the' from the sentence

Co-Authored-By: Oliver Eyton-Williams <ojeytonwilliams@gmail.com>

Co-authored-by: Oliver Eyton-Williams <ojeytonwilliams@gmail.com>

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-data-structures/iterate-through-all-an-arrays-items-using-for-loops.english.md

@@ -61,13 +61,12 @@ tests:
 ```js
 function filteredArray(arr, elem) {
   let newArr = [];
-  // change code below this line
+  // Only change code below this line
 
-  // change code above this line
+  // Only change code above this line
   return newArr;
 }
 
-// change code here to test different cases:
 console.log(filteredArray([[3, 2, 3], [1, 6, 3], [3, 13, 26], [19, 3, 9]], 3));
 ```
 
@@ -83,13 +82,11 @@ console.log(filteredArray([[3, 2, 3], [1, 6, 3], [3, 13, 26], [19, 3, 9]], 3));
 ```js
 function filteredArray(arr, elem) {
   let newArr = [];
-  // change code below this line
   for (let i = 0; i<arr.length; i++) {
     if (arr[i].indexOf(elem) < 0) {
       newArr.push(arr[i]);
     }
   }
-  // change code above this line
   return newArr;
 }
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-data-structures/iterate-through-the-keys-of-an-object-with-a-for...in-statement.english.md

@@ -72,9 +72,9 @@ tests:
 
 ```js
 function countOnline(usersObj) {
-  // change code below this line
+  // Only change code below this line
 
-  // change code above this line
+  // Only change code above this line
 }
 ```
 

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-data-structures/modify-an-array-stored-in-an-object.english.md

@@ -58,9 +58,9 @@ let user = {
 };
 
 function addFriend(userObj, friend) {
-  // change code below this line
+  // Only change code below this line
 
-  // change code above this line
+  // Only change code above this line
 }
 
 console.log(addFriend(user, 'Pete'));

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-data-structures/modify-an-object-nested-within-an-object.english.md

@@ -65,9 +65,9 @@ let userActivity = {
   }
 };
 
-// change code below this line
+// Only change code below this line
 
-// change code above this line
+// Only change code above this line
 
 console.log(userActivity);
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-data-structures/use-the-delete-keyword-to-remove-object-properties.english.md

@@ -51,9 +51,9 @@ let foods = {
   strawberries: 27
 };
 
-// change code below this line
+// Only change code below this line
 
-// change code above this line
+// Only change code above this line
 
 console.log(foods);
 ```