Danger of damaging 13" macbook pro by charging it with 85w charger?
No.  You cannot damage a laptop by charging it with a charger rated more than what it originally came with.

When a device has a power requirement of 10W it means it will only draw up to 10W.  A power supply with a rating of 45W will supply up to 45W.1 

A general rule of thumb is that you can always get a bigger power supply, never smaller.  Think of it like your electrical circuits in your house.  In the US, it's common to have 15A or 20A circuits.  Can you plug in vacuum cleaner that uses 12A?  Yup.  Can you run 2 at a time (24A) on the same circuit?  Nope, it will pop.  Can you run 1 vacuum and a 1A lightbulb (13A)?  Sure.

So, you can plug a device with a 60W draw into an 80W power supply, but it's not recommended to plug the same device with a 60W draw into a 45W power supply.

What can happen?

With the new USB-C ports on the Mac, most likely a slow charge.  With devices in general - you could damage/destroy the device and/or the power supply.



1 This assumes the same voltage.  USB-C will auto negotiate the power delivery.  Older devices that don't do this; too many volts can fry your device.  More amps than necessary won't harm anything.   Also see:  Choosing power supply, how to get the voltage and current ratings?