remove duplicate entries from tmpfiles

These directories are already specified in the upstream file /usr/lib/tmpfiles.d/nut-common-tmpfiles.conf and systemd prints a warning:

/usr/lib/tmpfiles.d/nut.conf:1: Duplicate line for path "/run/nut", ignoring. /usr/lib/tmpfiles.d/nut.conf:2: Duplicate line for path "/var/lib/nut", ignoring.

Resolves #2