Remove error that cannot appear anymore

Now that we do not support the old syntax for splicing types it is not
possible to get this error. The code is buggy and fails with another
error that is not worth testing.

Author: nicolasstucki

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -1906,8 +1906,6 @@ object desugar {
         new UntypedTreeTraverser {
           def traverse(tree: untpd.Tree)(using Context): Unit = tree match {
             case Splice(expr) => collect(expr)
-            case TypSplice(expr) =>
-              report.error(TypeSpliceInValPattern(expr), tree.srcPos)
             case _ => traverseChildren(tree)
           }
         }.traverse(expr)

compiler/src/dotty/tools/dotc/reporting/ErrorMessageID.scala

@@ -163,7 +163,7 @@ enum ErrorMessageID extends java.lang.Enum[ErrorMessageID]:
     ExtensionCanOnlyHaveDefsID,
     UnexpectedPatternForSummonFromID,
     AnonymousInstanceCannotBeEmptyID,
-    TypeSpliceInValPatternID,
+    TypeSpliceInValPatternID, // Error does not exist anymore
     ModifierNotAllowedForDefinitionID,
     CannotExtendJavaEnumID,
     InvalidReferenceInImplicitNotFoundAnnotationID,

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -2478,15 +2478,6 @@ import transform.SymUtils._
            |""".stripMargin
   }
 
-  class TypeSpliceInValPattern(expr:  untpd.Tree)(using Context)
-    extends SyntaxMsg(TypeSpliceInValPatternID) {
-    def msg = "Type splices cannot be used in val patterns. Consider using `match` instead."
-    def explain =
-      em"""|Type splice: `$$${expr.show}` cannot be used in a `val` pattern. Consider rewriting the `val` pattern
-           |as a `match` with a corresponding `case` to replace the `val`.
-           |""".stripMargin
-  }
-
   class ModifierNotAllowedForDefinition(flag: Flag)(using Context)
     extends SyntaxMsg(ModifierNotAllowedForDefinitionID) {
     def msg = em"Modifier ${hl(flag.flagsString)} is not allowed for this definition"