Revert "Allow center to be passed to toZXY()."
Revert "Allow center to be passed to toZXY()."

This reverts commit f251770fe8354ec7570cb5fe87f69f70731241df.

frankrowe/tilestream,staltz/tilestream,HydroLogic/tilestream,mapbox/tilestream,mapbox/tilestream,NolaMark/tilestream,simonpoole/tilestream,frankrowe/tilestream,NolaMark/tilestream,makinacorpus/tilestream,staltz/tilestream,makinacorpus/tilestream,markng/tilestream,HydroLogic/tilestream,zhm/tilestream,zhm/tilestream,markng/tilestream,simonpoole/tilestream