Can't remove line enters from styled email when forwarding

**Describe the bug**
When you forward an email and try to edit the email content, some lines can't be deleted; you can delete the content but not the line enter

**To Reproduce**
Steps to reproduce the behavior:
1. Forward a styled email
2. try deleting all the line rows

**Expected behavior**
It's expected that every line enter will be removed as well as the content

**Device and System information (please complete the following information):**
- Device: iPhone X

首先在 iPhone X 上复现该问题：转发一封样式化的电子邮件，编辑其内容，并尝试删除所有行。跟踪处理样式化消息的转发和电子邮件编辑入口点。完成的标准是删除内容时也会移除所有剩余的换行符。

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