Google Previes should be removed by AdBlockPlus or UsersScript, not a Greasemonkey script. It is just tree elements that have to be blocked.
You can add these three to AdblockPlus just by coping them to your filters one by one
Check what works better for you.
Hides the stupid "instant previews" and the magnifying glass icon, but you have to click "disable instant previews" every time you refresh the page. Would be perfect if instant previews were disabled by default, and you had to click to enable them if you wanted.