Revert "build-sys: include PolicyKit files as part of distribution"

This reverts commit 0c26bfc3d21fdb3963f1248c237e2f1a33b5566d.

src/core/org.freedesktop.systemd1.policy.in.in depends on values which
are specified at configure time, so we cannot ship the corresponding
policy file in the tarball.

Since we need to regenerate one policy file, we might as well generate
them all.
build-sys: Do not distribute generated emergency.service

It is already in nodist_systemunit_DATA and if it is
shipped, it contains the hardcoded path to systemctl
which will cause it to fail to start when
rootprefix != prefix and rootbindir != bindir.