Kill full sitemap cron generation

[mjangda]

For really large datasets, this ends up in a flood of thousands of cron events that can slow down or completely disable a site.

Fixes #81

[mjangda]

This keeps the ongoing cron-based updates (triggered every 15 minutes) although can be replaced with your own system, see https://github.com/Automattic/msm-sitemap/blob/master/wpcom-helper.php#L3

[pkevan]

Wouldn't this change result in lots of queued crons, but no action to execute them?

msm_cron_generate_sitemap_for_year_month_day should follow something similar to https://github.com/Automattic/msm-sitemap/blob/master/vipgo-helper.php#L8 unless I've misread the changeset.

[mjangda]

Wouldn't this change result in lots of queued crons, but no action to execute them?

Yep, great catch. I've restored the relevant code. A few other things we probably need to do:

• [ ] Update tests.
• [ ] Make sure wpcom-helper.php doesn't need any more changes.
• [ ] Remove any related options from other files.