bug(markdown) removing block quote on fenced code section doesnt remove blockquotes on fence lines

[yellis]

Describe the bug
In MD, when removing a block quote from a fenced code section, it only removes the opening > chars from the content lines, but not from the code fence lines.

Works fine in RT mode.

To Reproduce
Steps to reproduce the behavior:

1. Go to MD, add in this content:

```
Some code
```

2. select all, ctrl-q to apply blockquote, ctrl-q to remove blockquote
3. Now looks like this

>```
Some code
>```

Expected behavior
Should look like this:

```
Some code
```

Desktop (please complete the following information):
Windows 11 Chrome 103

Additional context
https://meta.stackexchange.com/a/380331/51

[yellis]

Related to #70, might be fixed when we fix there