Remove unused combination evidence and helpers

internal/engine/compose.go

@@ -483,21 +483,6 @@ func allMappingClaims(claims []compositionClaim) bool {
 	return true
 }
 
-func mergeDisjointMappings(target, incoming *document.Node, index *mappingIndex) {
-	for _, incomingEntry := range incoming.Mapping {
-		position := index.find(target, incomingEntry.Key)
-		if position < 0 {
-			cloned := incomingEntry
-			cloned.Value = document.Clone(incomingEntry.Value)
-			index.append(target, cloned)
-			continue
-		}
-		// Claim validation guarantees that the only remaining overlap is a
-		// mapping pair. Empty mappings naturally contribute no child entries.
-		mergeDisjointMappings(target.Mapping[position].Value, incomingEntry.Value, index)
-	}
-}
-
 func documentEntryIndex(entries []document.Entry, key string) int {
 	for index := range entries {
 		if entries[index].Key == key {