Naively use tail since head output is the first one

hydra-plutus/src/Hydra/Contract/Head.hs

@@ -185,24 +185,20 @@ checkCollectCom ctx@ScriptContext{scriptContextTxInfo = txInfo} (contestationPer
   (expectedChangeValue, collectedCommits, nTotalCommits) =
     traverseInputs
       (negate (txInfoAdaFee txInfo), [], 0)
-      (txInfoInputs txInfo)
+      -- we assume head output is always the first one so it is ok to use 'tail' here
+      (tail $ txInfoInputs txInfo)
 
   expectedOutputDatum :: Datum
   expectedOutputDatum =
     let utxoHash = hashPreSerializedCommits collectedCommits
      in Datum $ toBuiltinData Open{parties, utxoHash, contestationPeriod, headId = headId}
 
   -- Collect fuel and commits from resolved inputs. Any output containing a PT
-  -- is treated as a commit, "our" output is the head output and all remaining
-  -- will be accumulated as 'fuel'.
+  -- is treated as a commit and all remaining will be accumulated as 'fuel'.
   traverseInputs (fuel, commits, nCommits) = \case
     [] ->
       (fuel, commits, nCommits)
     TxInInfo{txInInfoResolved} : rest
-      | isHeadOutput txInInfoResolved ->
-        traverseInputs
-          (fuel, commits, nCommits)
-          rest
       | hasPT headId txInInfoResolved ->
         case commitDatum txInfo txInInfoResolved of
           Just commit@Commit{} ->
@@ -217,8 +213,6 @@ checkCollectCom ctx@ScriptContext{scriptContextTxInfo = txInfo} (contestationPer
         traverseInputs
           (fuel + txOutAdaValue txInInfoResolved, commits, nCommits)
           rest
-
-  isHeadOutput txOut = txOutAddress txOut == headAddress
 {-# INLINEABLE checkCollectCom #-}
 
 -- | Try to find the commit datum in the input and