[Blink] Produces extra span with line-height upon line join

[Marek Lewandowski]

since: 4.0 until master

1. open any sample with CKEditor (i.e. samples/replacebyclass.html)
2. set content to following content:

<p>aaaa</p>

3. place caret in: aa|aa
4. press enter
5. press backspace
6. press right arrow
7. check source code

Expected result:
Produced source code:

<p>aaaa</p>

Current result:
Code without checked attribute:

<p>aa<span style="line-height:1.6em">aa</span></p>

As far as I tested, the issue was not present in 3.6.6.1.

[Piotrek Koszuliński]

DUP of #9998. It's one of the cases mentioned there.