message: Replace eventIsReply util with replyEventId getter
diff: @@ -43,11 +43,6 @@ import QuestionDialog from "../dialogs/QuestionDialog";
  import { ActionPayload } from "../../../dispatcher/payloads";
  import AccessibleButton from '../elements/AccessibleButton';
  -function eventIsReply(mxEvent: MatrixEvent): boolean {
  - const relatesTo = mxEvent.getContent()["m.relates_to"];
  - return !!(relatesTo && relatesTo["m.in_reply_to"]);
  -}
  -
  function getHtmlReplyFallback(mxEvent: MatrixEvent): string {
  const html = mxEvent.getContent().formatted_body;
  if (!html) {
  @@ -72,7 +67,7 @@ function createEditContent(model: EditorModel, editedEvent: MatrixEvent): IConte
  if (isEmote) {
  model = stripEmoteCommand(model);
  }
  - const isReply = eventIsReply(editedEvent);
  + const isReply = !!editedEvent.replyEventId;
  let plainPrefix = "";
  let htmlPrefix = "";
  