Rewrite description for process_membership scheduled job

Text for this schedule job "Update Membership Statuses and Send Renewal Reminders" is no longer accurate.

Updates membership statuses and conditionally sends renewal reminders. WARNING: Membership renewal reminders are being migrated to the Schedule Reminders functionality which supports multiple renewal reminders. This job will be obsoleted in 4.3.

I vote that the new title should be "Update Membership Statuses" because this is what it does now, and this job is still necessary.

The new description should be:

Updates membership statuses, e.g. "current", "expired". WARNING: As of version 4.3, membership renewal reminders have been migrated to the Send Scheduled Reminders job which supports configurable, multiple membership renewal reminders.