How I Tested:
Logged in to https://qa2-us.nightly.sakaiproject.org/ as Admin.
Clicked the Checkbox next to TurnitinLTI
Scrolled to the bottom of the screen, clicked "Update Preferences"
Clicked on Sites Grid in upper right corner, scanned sites, TurnitinLTI site still visible.
Typed TurnitinLTI into filter box, site still visible there too.
Expected Results: Checking the box next to a site in My Preferences > Sites and Updating Preferences hides the site from the Sites Drawer.