Download a stock rom. Unzip and copy its hosts file over your current one.
Or have you tried reinstalling the app? I'd expect it would be able to restore the original...
Factory reset only wipes the data partition. Hosts is in the system partition so factory resetting will have no effect.
---------- Post added at 04:25 PM ---------- Previous post was at 04:24 PM ----------
If all else fails you can reflash your rom, or flash stock firmware via odin.