Remove map center env key from .env.example

These key need to be removed if we want to use
default leaflet config default value.

.env.example

@@ -37,6 +37,3 @@ PUSHER_APP_CLUSTER=mt1
 
 MIX_PUSHER_APP_KEY="${PUSHER_APP_KEY}"
 MIX_PUSHER_APP_CLUSTER="${PUSHER_APP_CLUSTER}"
-
-MAP_CENTER_LATITUDE=
-MAP_CENTER_LONGITUDE=