Fix incorrect license reference

Hi,

We are considering starting a new project and to use Kea as part of it. During our preliminary license check we found that there are a few files in Kea base package that have this in their license field:

// This Source Code Form is subject to the terms of the End User License
// Agreement. See COPYING file in the premium/ directory.

Above was taken from src/hooks/dhcp/lease_cmds/lease_cmds_callouts.cc
Also present in:
src/hooks/dhcp/stat_cmds/stat_cmds_callouts.cc
src/lib/dhcpsrv/cache_host_data_source.h

However, we cannot find this premium/ folder and the EULA either. Can the EULA be accessed through some other means, f.ex. in some other repo?

Thanks!

Br,
Juhani Heliö