Network: use F#'s ChunkBySize method

This commit removes the chunk helper function
in favor the already existing F# method named
ChunkBySize, not sure why I didn't find it before.

NOnion/Network/TorStream.fs

@@ -92,7 +92,7 @@ type TorStream(circuit: TorCircuit) =
                         data
                         |> Seq.skip offset
                         |> Seq.take length
-                        |> SeqUtils.Chunk Constants.MaximumRelayPayloadLength
+                        |> Seq.chunkBySize Constants.MaximumRelayPayloadLength
 
                     let rec sendChunks dataChunks =
                         async {

NOnion/Utility/SeqUtils.fs

@@ -1,12 +1,5 @@
 namespace NOnion.Utility
 
 module SeqUtils =
-    // Helper function copied from https://stackoverflow.com/a/21615676
-    let Chunk chunkSize sequence =
-        sequence
-        |> Seq.mapi(fun i x -> i / chunkSize, x)
-        |> Seq.groupBy fst
-        |> Seq.map(fun (_, g) -> Seq.map snd g)
-
     let TakeRandom count sequence =
         sequence |> Seq.sortBy(fun _ -> System.Guid.NewGuid()) |> Seq.take count