How to disable Cortana in Windows 10 Anniversary Update (Pro and Enterprise editions)

First launch the group policy editor by pressing Windows R, type gpedit.msc

Navigate to Computer Configuration
Administrative Templates
Windows Components
Search

Locate the "Allow Cortana" setting and hit enter.

Set the Allow Cortana Option to Disable and enter on OK

You can now close the group policy editor.  You'll have to sign out and sign back in or restart your pc for this to take.