Revert "Add ability to duplicate layers. Refs #364."
Revert "Add ability to duplicate layers. Refs #364."

This reverts commit a462fd7f2a2a92080a52a053ac8fca088cf74140.

paulovieira/tilemill-clima,paulovieira/tilemill-clima,nyimbi/tilemill,nyimbi/tilemill,tizzybec/tilemill,nyimbi/tilemill,tilemill-project/tilemill,Zhao-Qi/tilemill,fxtentacle/tilemill,florianf/tileoven,paulovieira/tilemill-clima,Zhao-Qi/tilemill,Zhao-Qi/tilemill,fxtentacle/tilemill,nyimbi/tilemill,florianf/tileoven,isaacs/tilemill,fxtentacle/tilemill,mbrukman/tilemill,paulovieira/tilemill-clima,Teino1978-Corp/Teino1978-Corp-tilemill,tilemill-project/tilemill,Zhao-Qi/tilemill,mbrukman/tilemill,fxtentacle/tilemill,florianf/tileoven,tizzybec/tilemill,mbrukman/tilemill,tizzybec/tilemill,nyimbi/tilemill,paulovieira/tilemill-clima,tizzybec/tilemill,MappingKat/tilemill,mbrukman/tilemill,MappingKat/tilemill,tizzybec/tilemill,isaacs/tilemill,MappingKat/tilemill,fxtentacle/tilemill,tilemill-project/tilemill,mbrukman/tilemill,MappingKat/tilemill,Zhao-Qi/tilemill,isaacs/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,MappingKat/tilemill