It's actually not a HR tag, it's a CSS border. To remove it, in qa-styles.css find this block...
.qa-q-view-meta {
border-bottom: 1px solid #bdc3c7;
display: block;
}
...and remove the line starting "border-bottom".
Edit: here's an alternative that will survive upgrades to the theme. In the Admin area under Layout, add this to the box"Custom HTML in <head> section of every page"
<style>
.qa-q-view-meta {
border-bottom: 0;
}
</style>
