Admins can delete WhatsApp group messages.

With the new tool, group administrators will have more power in the Application.
The new function is being tested on WhatsApp and allows group administrators to be able to delete messages from any of the participants, so that others can no longer see them.
The feature can be used to delete offenses and inappropriate content in a group. Furthermore, when the message is deleted by the administrator, the other group participants will be alerted that that content was not deleted by the message author.
Source:
https://wabetainfo.com/whatsapp-beta-for-android-2-22-1-7-whats-new/