It relied on the now non-existing max-rgb plug-in, which was removed in commit
dd89f4a3. After some thoughts and discussions, the Predator script is fun, but
clearly not a mandatorily "needed" one here, which is why — instead of
re-integrating max-rgb —, I have decided to also remove Predator.

Both these script/plug-in are not totally dead. They were moved to the
gimp-data-extras repository and even ported to GIMP 3.0 API. They can be an
interesting use case for a fun extension to be installable through our future
extension platform. To be continued.