Remove obsolete @OptIn(ExperimentalStdlibApi::class) annotations

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

^KT-62510

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/MemoizedMultiFieldValueClassReplacements.kt

@@ -466,7 +466,6 @@ class MemoizedMultiFieldValueClassReplacements(
         }
     }
 
-    @OptIn(ExperimentalStdlibApi::class)
     private fun verifyStructureCompatibility(
         targetStructure: List<RemappedParameter>,
         sourceStructure: List<RemappedParameter>

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/ScriptGenerator.kt

@@ -43,7 +43,6 @@ import org.jetbrains.kotlin.resolve.calls.util.isSingleUnderscore
 import org.jetbrains.kotlin.utils.addIfNotNull
 
 internal class ScriptGenerator(declarationGenerator: DeclarationGenerator) : DeclarationGeneratorExtension(declarationGenerator) {
-    @OptIn(ExperimentalStdlibApi::class)
     fun generateScriptDeclaration(ktScript: KtScript): IrDeclaration? {
         val descriptor = getOrFail(BindingContext.DECLARATION_TO_DESCRIPTOR, ktScript) as ScriptDescriptor