Hey all, thanks for reaching out and flagging this change - the short answer is we intentionally removed the button because it was not functioning as expected.
Instead of previewing the effect of the query, it was fully running the raw SQL against the configured resource without any safeguards in place. This wasn't a big deal for anybody exclusively writing SELECT statements, but could have been quite bad for anybody writing potentially destructive queries.
To be clear, the Preview button in GUI mode is still working as expected, but we felt the need to take the preemptive measure of removing the button from the SQL view in order to prevent data loss.
I hope that clears up any confusion! Don't hesitate to follow up with any additional questions if there's anything I can help with.