Remove group node to avoid extra newline and indent

[ramya-rao-a]

Grouped abbreviations get expanded with an extra indent and a new line at the beginning
Example:
(ul>li)*2 gets expanded to

       <ul>
            <li></li>
       </ul>
       <ul>
            <li></li>
       </ul>

instead of

<ul>
     <li></li>
</ul>
<ul>
     <li></li>
</ul>

This is due to the group node.
I tried to update the markup-formatter module to ignore the group node.
But it got too messy.
So I propose to fix it in the abbreviation model itself.

[ramya-rao-a]

cc @sergeche