Remove Reports Default post_parent.

The post_parent = 0 in, would shows only top level posts, which in Payment Errors\Logs would mean that it will not return any payment errors attached(children) to a Payment.
If omitted, all payment errors/logs will be shown and will not affect other requests since they have parent post filter or are top level posts in the first place. 
Merge pull request #737 from vanbo/master

Remove Reports Log Default post_parent.