Remove dead code

Author: whyoleg

core/commonMain/src/kotlinx/serialization/modules/PolymorphicModuleBuilder.kt

@@ -21,7 +21,6 @@ public class PolymorphicModuleBuilder<in Base : Any> @PublishedApi internal cons
     private val baseSerializer: KSerializer<Base>? = null
 ) {
     private val subclasses: MutableList<Pair<KClass<out Base>, KSerializer<out Base>>> = mutableListOf()
-    private var defaultSerializerProvider: ((Base) -> SerializationStrategy<Base>?)? = null
     private var defaultDeserializerProvider: ((String?) -> DeserializationStrategy<Base>?)? = null
 
 
@@ -84,15 +83,15 @@ public class PolymorphicModuleBuilder<in Base : Any> @PublishedApi internal cons
      * 
      */
     @ExperimentalSerializationApi
-    public fun <T: Base> subclassesOfSealed(serializer: KSerializer<T>) {
+    public fun <T : Base> subclassesOfSealed(serializer: KSerializer<T>) {
         // Note that the parameter type is `KSerializer` as `SealedClassSerializer` is an internal type
         // not available to users
         require(serializer is SealedClassSerializer) {
             "subclassesOfSealed only supports automatic adding of subclasses of sealed types with standard serializers."
         }
         for ((subsubclass, subserializer) in serializer.class2Serializer.entries) {
             // This error would be caught by the Json format in its validation, but this is format specific
-            require (subserializer.descriptor.kind != PolymorphicKind.OPEN) {
+            require(subserializer.descriptor.kind != PolymorphicKind.OPEN) {
                 "It is not possible to register subclasses (${serializer.descriptor.serialName}) of sealed types when those subclasses " +
                     "themselves are (open) polymorphic, as this would represent an incomplete hierarchy."
             }
@@ -172,11 +171,6 @@ public class PolymorphicModuleBuilder<in Base : Any> @PublishedApi internal cons
             )
         }
 
-        val defaultSerializer = defaultSerializerProvider
-        if (defaultSerializer != null) {
-            builder.registerDefaultPolymorphicSerializer(baseClass, defaultSerializer, false)
-        }
-
         val defaultDeserializer = defaultDeserializerProvider
         if (defaultDeserializer != null) {
             builder.registerDefaultPolymorphicDeserializer(baseClass, defaultDeserializer, false)