Your attribute counting your enemy race kills has been transferred to your character's internal information under the title of Kill count.
All new kills, so-called scalps, will be counted from 0 and shown in your character's open information.
Old scalps can be used as before - for quests, for valour etc.
The changes have been made to allow for technical changes and developments.
Your attribute has not been deleted or reset! It has simply been hidden from your public information. You can still your old scalp count in the personal information of your character, via your character backpack.