This is currently an outstanding feature request (acknowledged by Google), issue 3760.

Here's my solution: http://jsbin.com/ajimur/10. It uses a function that adds a delete button to the passed in polygon (below the undo button).

Alternatively, someone suggested this approach: right-click to delete closest vertex, which works fine but is somewhat lacking in UI finesse. I built on the code from the link to check if the click was inside (or within 1 pixel of) the node - in a JSBin here: http://jsbin.com/ajimur/.

EDIT: as Amr Bekhit pointed out - this approach is currently broken, as the events need to be attached to the polygon.