[#3289] Wrong message for empty contact category list

#### Steps to reproduce the issue
On clean j323 install with learning demo data create a menu item to contact category C
Pick the menu item in the frontend and see: No articles to display



#### Expected result
To see: There are no Contacts to display
text from COM_CONTACT_NO_CONTACTS instead of COM_CONTACT_NO_ARTICLES


#### Actual result
You get: No articles to display


#### System information (as much as possible)
Clean J323 install with learning demo data.


#### Additional comments
Replacing COM_CONTACT_NO_ARTICLES with COM_CONTACT_NO_CONTACTS makes COM_CONTACT_NO_ARTICLES unused, which normally should have it removed.
Considering that articles are also shown for contacts it might be intended to be used.
Separate issue I think, removing/using.