Allow systemd to mask postgresql service file

[kimsondrup]

When masking the postgresql service with systemd a symlink pointing to /dev/null will be created at /etc/systemd/system/${service_name}.service

This pull request is to ensure Postgresql Puppet module to not try to undo the masking by removing the symlink.

[puppet-community-rangefinder]

postgresql::server::config is a class

that may have no external impact to Forge modules.

This module is declared in 70 of 578 indexed public Puppetfiles.

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These results were generated with Rangefinder, a tool that helps predict the downstream impact of breaking changes to elements used in Puppet modules. You can run this on the command line to get a full report.

Exact matches are those that we can positively identify via namespace and the declaring modules' metadata. Non-namespaced items, such as Puppet 3.x functions, will always be reported as near matches only.

[CLAassistant]

All committers have signed the CLA.

[ekohl]

This looks ok to me. I've started CI.