fix: #20200212 已创建课时不允许修改班型

因网校部分直播课程在已创建的课时后无法对班型进行修改，提现为修改班型成功但是直播教师未改变，所以对相关的代码进行屏蔽

web/activities/live/resources/views/create_or_update_body.html.twig

  {% set roomTypes = get_live_room_type() %}
  {% if roomTypes and not activity.id|default(false) %}
    <div class="form-group">
      <div class="col-sm-2 control-label">
        <label for="roomType">{{ 'course.live_activity.room_type'|trans }}</label>
      </div>
      <div class="col-sm-10">
        <select class="form-control width-input" name="roomType" {% if not canUpdateRoomType|default(1) %}disabled{% endif %}>
          {% for key, roomType in roomTypes if roomTypes %}
            <option value="{{ key }}" {% if activity.ext.roomType|default('large') == key %}selected{% endif %}>{{ roomType|trans }}</option>
          {% endfor %}
        </select>
      </div>
    </div>
  {% endif %}