Correct heading description in Array.p.slice() doc (mdn#2679)

* Correct heading description in Array.p.slice() doc

This is a follow-up fix to mdn#1351

* Sync up heading IDs with heading-text change

files/en-us/web/javascript/reference/global_objects/array/splice/index.html

@@ -128,7 +128,7 @@ <h3 id="Remove_2_elements_from_index_0_and_insert_parrot_anemone_and_blue">Remov
 // myFish is ["parrot", "anemone", "blue", "trumpet", "sturgeon"]
 // removed is ["angel", "clown"]</pre>
 
-<h3 id="Remove_2_elements_before_index_2">Remove 2 elements before index 2</h3>
+<h3 id="remove_2_elements_starting_from_index_2">Remove 2 elements, starting from index 2</h3>
 
 <pre class="brush: js">let myFish = ['parrot', 'anemone', 'blue', 'trumpet', 'sturgeon']
 let removed = myFish.splice(2, 2)
@@ -144,7 +144,7 @@ <h3 id="Remove_1_element_from_index_-2">Remove 1 element from index -2</h3>
 // myFish is ["angel", "clown", "sturgeon"]
 // removed is ["mandarin"]</pre>
 
-<h3 id="Remove_all_elements_before_index_2">Remove all elements before index 2</h3>
+<h3 id="remove_all_elements_starting_from_index_2">Remove all elements, starting from index 2</h3>
 
 <pre class="brush: js">let myFish = ['angel', 'clown', 'mandarin', 'sturgeon']
 let removed = myFish.splice(2)