Remove the `No message history available` message

It's misleading because it shows before MAM has finished (which also causes
flashing)

Showing it only after MAM has finished would be preferable but too much
work, so I'm removing it for now.

src/shared/chat/message-history.js

@@ -2,13 +2,10 @@ import "./message";
 import dayjs from 'dayjs';
 import tpl_new_day from "templates/new_day.js";
 import { CustomElement } from 'components/element.js';
-import { __ } from 'i18n';
 import { _converse, api } from "@converse/headless/core";
 import { html } from 'lit-element';
 import { repeat } from 'lit-html/directives/repeat.js';
 
-const i18n_no_history = __('No message history available.');
-
 const tpl_message = (o) => html`
     <converse-chat-message
         .hats=${o.hats}
@@ -115,9 +112,7 @@ export default class MessageHistory extends CustomElement {
 
     render () {
         const msgs = this.messages;
-        return msgs.length ?
-            html`${repeat(msgs, m => m.get('id'), m => this.renderMessage(m)) }` :
-            html`<div class="empty-history-feedback form-help"><span>${i18n_no_history}</span></div>`;
+        return msgs.length ? html`${repeat(msgs, m => m.get('id'), m => this.renderMessage(m)) }` : '';
     }
 
     renderMessage (model) {