protobuf: build with up-to-date dateutil

Fixes #32571. @mistydemeo, can you take a look / try this?
The developers have never responded to any Google Code tickets and the oldest is from 2010 so we might need to apply a more personal touch if we want a response. (My experience with dateutil is that the <2 restriction is very likely a historical artifact and is that this is unlikely to cause problems.)