Looks like one can no longer delete themes from admin in 3.8--only add, activate, and preview.
Sometimes I preview a number of themes before settling on one to customize. I don't want to keep the others around later--they only pester me with meaningless "update" notices.
I'm quite capable of deleting unwanted themes from my websites directly, but taking away a simple convenience seems unwarranted. Could we have the "delete" button back, please?