Remove memcached support

Apparently we had memcached support. It was never worth it, and put
a weird md5 hash calculation in the path of regular caching. Seeing
as it was completely undocumented, I doubt anyone has ever used it.

overviewer_core/world.py

@@ -731,7 +731,7 @@ class CachedRegionSet(RegionSetWrapper):
         self.key = s
 
     def get_chunk(self, x, z):
-        key = hashlib.md5(repr((self.key, x, z))).hexdigest()
+        key = (self.key, x, z)
         for i, cache in enumerate(self.caches):
             try:
                 retval = cache[key]