Fix comment thread update handler

When comment thread update comes, the code would go
through deleted and remaining comments. The bug was that
if there was a deleted comment, the code would delete all the comments
in the thread past the deleted comment as well,
and then would erroneousely consider remaining comments as new ones,
basically duplicating them in UI.

Fix for #64042

src/vs/workbench/parts/comments/electron-browser/commentThreadWidget.ts

@@ -236,7 +236,7 @@ export class ReviewZoneWidget extends ZoneWidget {
 
 		// del removed elements
 		for (let i = commentElementsToDel.length - 1; i >= 0; i--) {
-			this._commentElements.splice(commentElementsToDelIndex[i]);
+			this._commentElements.splice(commentElementsToDelIndex[i], 1);
 			this._commentsElement.removeChild(commentElementsToDel[i].domNode);
 		}