Update error msg for Parsers.scala:1738 and 1739

These error messages are for aux ctors needing non-implicit params. I'm testing the error messages with this code

```
class Square(val len: Int) {
  // typical cases:
  //  (1) this() parens are forgotten, (2) argument set as implicit
  def this(implicit width: Double) = this(0)
  def this = { this(4) }
}

class MyList(val s: String) {
  def this
```

1 files changed, 2 insertions, 2 deletions

diff --git a/src/dotty/tools/dotc/parsing/Parsers.scala b/src/dotty/tools/dotc/parsing/Parsers.scala
index 4926ebb9f..95626846d 100644
--- a/src/dotty/tools/dotc/parsing/Parsers.scala
+++ b/src/dotty/tools/dotc/parsing/Parsers.scala
@@ -1742,8 +1742,8 @@ object Parsers {
       if (owner == nme.CONSTRUCTOR && (result.isEmpty || (result.head take 1 exists (_.mods is Implicit)))) {
         in.token match {
           case LBRACKET   => syntaxError("no type parameters allowed here")
-          case EOF        => incompleteInputError("auxiliary constructor needs non-implicit parameter list")
-          case _          => syntaxError("auxiliary constructor needs non-implicit parameter list", start)
+          case EOF        => incompleteInputError(AuxConstructorNeedsNonImplicitParameter())
+          case _          => syntaxError(AuxConstructorNeedsNonImplicitParameter(), start)
         }
       }
       result