Remove remaining v5 cron entries once v5 is decommissioned

[simongray]

The remaining entries in /etc/cron.d/dspace were kept because v5 is still live. Once v5 is decommissioned, remove them:

• pg_dump entries — daily dumps of the v5 dspace and dspace-utils databases (run as zgk261). Safe to remove once the v5 PostgreSQL instance is no longer being updated.
• backup2l entry — weekly backup of /opt/clarindk-dspace files. Safe to remove once v5 is decommissioned.

At that point /etc/cron.d/dspace can be deleted entirely.

[simongray]

Done. Backed up the old cron files to /opt/dspace7/ + the old NGINX files.