Remove unnecessary upcast and add missing helper

docs/conceptual/snippets/fssequences/snippet180.fs

@@ -1,10 +1,14 @@
+    let printSeq seq1 = 
+      for v in seq1 do printf "%A " v
+      printfn ""
 
-    let seqNumbers = [ 1.0; 1.5; 2.0; 1.5; 1.0; 1.5 ] :> seq<float>
+    let seqNumbers = [ 1.0; 1.5; 2.0; 1.5; 1.0; 1.5 ]
     let seqWindows = Seq.windowed 3 seqNumbers
     let seqMovingAverage = Seq.map Array.average seqWindows
+
     printfn "Initial sequence: "
     printSeq seqNumbers
     printfn "\nWindows of length 3: "
     printSeq seqWindows
     printfn "\nMoving average: "
-    printSeq seqMovingAverage
+    printSeq seqMovingAverage