According to Apple Support, there are two shortcuts for shutdown:
Control–Option–Command–Power button or
I tried the power-button shortcut on my MacBook Pro Mid 2012 with macOS Sierra 10.12.4 and it worked similar to the old eject-button shortcut (maybe a little slower, but that could be the new OS). I assume Apple added the additional shortcut for newer devices that don't have optical drives and eject buttons, but they neglected to maintain the eject-button shortcut for the older machines within the Sierra update. Just more infinite wisdom from Apple.
UPDATE: I found that the standard Control–Option–Command–Media Eject does indeed work with Sierra. It seems that, at least on my machine, the key remapping program Karabiner and the Sierra-compatible version Karabiner Elements causes the Eject button to not register at all. When I disable Karabiner, the shutdown shortcut works normally. I did, however, find that Karabiner Elements does allow another key to be remapped as Eject. This won't work well on the limited internal keyboard, but for the external wired keyboard I set up one of the useless function keys (F19) as the Eject button. Now, Control–Option–Command–F19 works with the external keyboard and shuts down the computer.