Clear unused scheduled events in wp_options cron.

[bi0xid]

Clears unused scheduled events in wp_options cron before adding a new scheduled event. Prevents server exhaustion and several problems when having heavy loads of information in wp_options cron.

Solves https://disqus.com/home/channel/discussdisqus/discussion/channel-discuss disqus/tons_of_dsq_sync_forum_entries_in_cron_row_wp_options_and_10x_ser ver_loads/ Solves https://wordpress.org/support/topic/high-server-load-and-dsq_sync_forum- problem

[archon810]

This will just continue clearing and postponing and never running the Disqus sync cron job on a busy server.