fix: consolidate misc comments (#39583)

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/concatenating-strings-with-plus-operator.english.md

@@ -55,7 +55,7 @@ tests:
 <div id='js-seed'>
 
 ```js
-var myStr; // Only change this line
+var myStr; // Change this line
 
 ```
 

curriculum/challenges/english/03-front-end-libraries/react-and-redux/moving-forward-from-here.english.md

@@ -60,6 +60,8 @@ ReactDOM.render(
 );
 */
 
+// Only change code below this line
+
 ```
 
 </div>

curriculum/challenges/english/03-front-end-libraries/sass/split-your-styles-into-smaller-chunks-with-partials.english.md

@@ -43,9 +43,7 @@ tests:
 <div id='html-seed'>
 
 ```html
-// The main.scss file
-
-
+<!-- The main.scss file -->
 
 
 ```
@@ -60,7 +58,6 @@ tests:
 <section id='solution'>
 
 ```html
-// The main.scss file
 @import 'variables'
 ```