fix(contrib/init/systemd): remove mount rprivate

Docker does this now via 157d99a72786c454dfaad8b0800914cc80879aa8

Docker-DCO-1.1-Signed-off-by: Brandon Philips <brandon.philips@coreos.com> (github: philips)

contrib/init/systemd/socket-activation/docker.service

@@ -4,7 +4,6 @@ Documentation=http://docs.docker.io
 After=network.target
 
 [Service]
-ExecStartPre=/bin/mount --make-rprivate /
 ExecStart=/usr/bin/docker -d -H fd://
 
 [Install]