PhotonDetectors directory is duplicated from duneprototypes

[calcuttj]

The PhotonDetectors directory in this repo is a seeming duplicate of the one in duneprototypes

We should trim this down @yangtj207 @tomjunk any preference/idea?

[yangtj207]

There is also protodune photon detector code in this repository:
https://github.com/DUNE/duneopdet/tree/develop/duneopdet/OpticalDetector