Stabilize SIP-53 (quote pattern explicit type variable syntax) (#18574)

SIP-53:
https://docs.scala-lang.org/sips/quote-pattern-type-variable-syntax.html

Follow up of  #17362 for 3.4

compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala

@@ -172,10 +172,6 @@ trait QuotesAndSplices {
 
     getQuotedPatternTypeVariable(tree.name.asTypeName) match
       case Some(typeSym) =>
-        checkExperimentalFeature(
-          "support for multiple references to the same type (without backticks) in quoted type patterns (SIP-53)",
-          tree.srcPos,
-          "\n\nSIP-53: https://docs.scala-lang.org/sips/quote-pattern-type-variable-syntax.html")
         warnOnInferredBounds(typeSym)
         ref(typeSym)
       case None =>
@@ -223,12 +219,6 @@ trait QuotesAndSplices {
       case LambdaTypeTree(_, body: TypeBoundsTree) => // ok
       case _ => report.error("Quote type variable definition cannot be an alias", tdef.srcPos)
 
-    if quoted.isType && untpdTypeVariables.nonEmpty then
-      checkExperimentalFeature(
-        "explicit type variable declarations quoted type patterns (SIP-53)",
-        untpdTypeVariables.head.srcPos,
-        "\n\nSIP-53: https://docs.scala-lang.org/sips/quote-pattern-type-variable-syntax.html")
-
     if ctx.mode.is(Mode.InPatternAlternative) then
       for tpVar <- untpdTypeVariables do
         report.error(IllegalVariableInPatternAlternative(tpVar.name), tpVar.srcPos)