Fixed sync of notes with <p> in code.

My notes with `<p>...</p>` in the code doesn't sync after being modified, I get the following message:
```
 [...] ( nixnote.cpp @ 1564 ) "Unable to update note.  Invalid note structure : "
```

I found what caused the problem and the fix was removing the line replacing all `<p>` with `</p>` in `void EnmlFormatter::postXmlFix()`

I think I found the commit that introduced this behavior 35b8d2829db4f4c0d9c0f3da67298d16b7674caf and the reasoning in the comment above the code is that any tags that doesn't end with `\>` will break the Qt parser. 

Removing this line did not introduce any new problems for me, I tried adding a faulty lone `<p>` without an `</p>` and the syncing still worked for me because Tidy caught this:
```
[...] ( html/enmlformatter.cpp @ 89 ) Tidy Errors: "line 9 column 109 - Warning: trimming empty <p>
```

When I inserted `<p/>` in the code Tidy seemed to just remove it with the same message as above.

Being completely new to the project I might have missed something, but I think it is safe to remove this line because Tidy catches any fixes any problems with `<p>` anyway.