Fix acceptance tests to use new syntax.

examples/hello_world/validators/hello_world.ak

@@ -1,6 +1,5 @@
 use aiken/hash.{Blake2b_224, Hash}
 use aiken/list
-use aiken/string
 use aiken/transaction.{ScriptContext}
 use aiken/transaction/credential.{VerificationKey}
 
@@ -14,7 +13,7 @@ type Redeemer {
 
 validator spend {
   fn(datum: Datum, redeemer: Redeemer, context: ScriptContext) -> Bool {
-    let must_say_hello = string.from_bytearray(redeemer.msg) == "Hello, World!"
+    let must_say_hello = redeemer.msg == "Hello, World!"
 
     let must_be_signed =
       list.has(context.transaction.extra_signatories, datum.owner)
@@ -22,4 +21,3 @@ validator spend {
     must_say_hello && must_be_signed
   }
 }
-