wp site empty should empty the sticky posts option too

[johnbillion]

Bug Report

• Yes, I reviewed the contribution guidelines.
• Yes, more specifically, I reviewed the guidelines on how to write clear bug reports.

Describe the current, buggy behavior

wp site empty doesn't clear the sticky_posts option, which means newly created posts can end up sticky if their ID matches an old sticky post before the site was emptied.

Describe how other contributors can replicate this bug

• Publish a post and make it sticky
• Run wp site empty
• Create a new post with the same ID as the previously sticky post
• Observe that the new post is unexpectedly sticky

Describe what you would expect as the correct outcome

The sticky_posts option should be cleared when the site is emptied.

[johnbillion]

Previously: #236