removing listBlockLocations by SE

@ticoann @ericvaandering 
this fixes issue #5264
Cleaning up and removing the ability to listBlockLocations by SE as should all be by PNN now. This obviously has to be merged after we are happy with all the other changes but since it's a quick one I did it now.

Note: I left the ability for the getReplicaSEForBlocks API from the PhEDEx service to return SEs incase it might be needed in the future but this is not used now in the DBS3Reade.