Fix invalid method mapping in compileSdk 35

Citing the documentation:

```
The List type in Java is mapped to the MutableList type in Kotlin. Because the List.removeFirst() and List.removeLast() APIs have been introduced in Android 15 (API level 35), the Kotlin compiler resolves function calls, for example list.removeFirst(), statically to the new List APIs instead of to the extension functions in kotlin-stdlib.

If an app is re-compiled with compileSdk set to 35 and minSdk set to 34 or lower, and then the app is run on Android 14 and lower, a runtime error is thrown:
```

https://developer.android.com/about/versions/15/behavior-changes-15

libs/fluxc-tests/src/test/java/org/wordpress/android/fluxc/comment/CommentSqlUtilsTest.kt

@@ -179,9 +179,9 @@ class CommentSqlUtilsTest {
         val commentsInDb = generateCommentModels(60, ALL)
         val remoteComments = generateCommentModels(30, ALL)
 
-        remoteComments.removeLast()
-        remoteComments.removeLast()
-        remoteComments.removeLast()
+        remoteComments.removeAt(remoteComments.lastIndex)
+        remoteComments.removeAt(remoteComments.lastIndex)
+        remoteComments.removeAt(remoteComments.lastIndex)
 
         commentsInDb.forEach {
             CommentSqlUtils.insertOrUpdateComment(it)
@@ -239,9 +239,9 @@ class CommentSqlUtilsTest {
         val remoteComments = generateCommentModels(50, ALL)
 
         // exclude first 3 comments
-        remoteComments.removeFirst()
-        remoteComments.removeFirst()
-        remoteComments.removeFirst()
+        remoteComments.removeAt(0)
+        remoteComments.removeAt(0)
+        remoteComments.removeAt(0)
 
         commentsInDb.forEach {
             CommentSqlUtils.insertOrUpdateComment(it)