This text is located within the language pack files. For more information on editing the language pack files, go here:
http://www.interspire.com/support/kb/questions/763/Editing+the+language+pack
Specifically, you can find the text inside the /includes/language/front_language.ini file. The line you're after should look like:
catNoArticlesInCategory = "No articles found in this category."
So if you want to remove it completely you can just leave it blank like this:
catNoArticlesInCategory = ""

The article has been updated successfully.