Remove obsolete @OptIn(ExperimentalStdlibApi::class) annotations

They were added when `buildList`, `buildMap` and `buildSet` were experimental.

^KT-62510

compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/LightTreePositioningStrategies.kt

@@ -1154,7 +1154,6 @@ object LightTreePositioningStrategies {
         }
     }
 
-    @OptIn(ExperimentalStdlibApi::class)
     val COMMAS: LightTreePositioningStrategy = object : LightTreePositioningStrategy() {
         override fun mark(
             node: LighterASTNode,

compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/PositioningStrategies.kt

@@ -1015,7 +1015,6 @@ object PositioningStrategies {
         }
     }
 
-    @OptIn(ExperimentalStdlibApi::class)
     val COMMAS: PositioningStrategy<PsiElement> = object : PositioningStrategy<PsiElement>() {
         override fun mark(element: PsiElement): List<TextRange> {
             return buildList {