Create a new DWORD called AllowDeleteUsers and set the value to 1 under:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Computer Telephony Solutions\ActiveDirectoryIntegration

Or for 32 bit system

If you set this DWORD registry value to 1 (at the server), and then login from call recording admin, you´ll find you´re able to delete an AD-imported user:

HKEY_LOCAL_MACHINE\SOFTWARE\Computer Telephony Solutions\ActiveDirectoryIntegration\AllowDeleteUsers