Bug#956795: libpam-systemd: fills the logs with messages about pam_systemd.so

[Francesco Potortì]

$ ldd /usr/sbin/cron
	linux-vdso.so.1 (0x00007ffdbad7f000)
	libpam.so.0 => /lib/x86_64-linux-gnu/libpam.so.0 (0x00007f9c76d08000)
	libselinux.so.1 => /lib/x86_64-linux-gnu/libselinux.so.1 (0x00007f9c76cdd000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f9c76b1a000)
	libaudit.so.1 => /lib/x86_64-linux-gnu/libaudit.so.1 (0x00007f9c76aef000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f9c76aea000)
	libpcre2-8.so.0 => /usr/lib/x86_64-linux-gnu/libpcre2-8.so.0 (0x00007f9c76a5a000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f9c76d5f000)
	libcap-ng.so.0 => /lib/x86_64-linux-gnu/libcap-ng.so.0 (0x00007f9c76a50000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f9c76a2f000)

$ apt-cache policy libpam0g
libpam0g:
  Installed: 1.3.1-5
  Candidate: 1.3.1-5
  Version table:
 *** 1.3.1-5 990
        990 http://ftp.it.debian.org/debian testing/main amd64 Packages
        101 http://ftp.it.debian.org/debian unstable/main amd64 Packages
        100 /var/lib/dpkg/status