Do not use nightlyBefore/ltsBefore

Handler/Feed.hs

@@ -52,10 +52,7 @@ mkFeed mBranch snaps = do
 
 getContent :: SnapshotId -> Snapshot -> Handler Html
 getContent sid2 snap = do
-    mprev <-
-        case snapshotName snap of
-            SNLts x y -> ltsBefore x y
-            SNNightly day -> nightlyBefore day
+    mprev <- snapshotBefore $ snapshotName snap
     case mprev of
         Nothing -> return "No previous snapshot found for comparison"
         Just (sid1, name1) -> do

Stackage/Database.hs

@@ -10,8 +10,6 @@ module Stackage.Database
     , newestNightly
     , ltsMajorVersions
     , snapshotBefore
-    , nightlyBefore
-    , ltsBefore
     , lookupSnapshot
     , snapshotTitle
     , PackageListingInfo (..)