There is no maintainer for xserver-xorg-core. This means that this package no longer exists (or never existed). Please do not report new bugs against this package.
You may want to refer to the following packages that are part of the same source: xdmx, xdmx-tools, xnest, xorg-server-source, xserver-common, xserver-xephyr, xserver-xorg-core-udeb, xserver-xorg-dev, xserver-xorg-legacy, xvfb, xwayland.
You might like to refer to the source package src:xorg-server's bug page.