Fix minor compile warnings

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/GeneratorHelpers.kt

@@ -475,7 +475,7 @@ interface IrBuilderExtension {
             compilerContext.externalSymbols.referenceClass(module.getClassFromInternalSerializationPackage(SpecialBuiltins.nullableSerializer))
         if (serializerClassOriginal == null) {
             if (genericIndex == null) return null
-            val thiz = enclosingGenerator.irClass.thisReceiver!!
+
             val prop = enclosingGenerator.localSerializersFieldsDescriptors[genericIndex]
             return irGetField(irGet(dispatchReceiverParameter), compilerContext.localSymbolTable.referenceField(prop).owner)
         }

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/SerializerIrGenerator.kt

@@ -176,7 +176,6 @@ class SerializerIrGenerator(val irClass: IrClass, override val compilerContext:
                 serializerTower(this@SerializerIrGenerator, irFun.dispatchReceiverParameter!!, it)) { "Property ${it.name} must have a serializer" }
         }
 
-        val kSer = serializableDescriptor.module.getClassFromSerializationPackage(KSERIALIZER_NAME.identifier)
         val kSerType = ((irFun.returnType as IrSimpleType).arguments.first() as IrTypeProjection).type
         val array = createArrayOfExpression(kSerType, allSerializers)
         +irReturn(array)

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/resolve/KSerializerDescriptorResolver.kt

@@ -350,14 +350,12 @@ object KSerializerDescriptorResolver {
         )
         val serializerClass = classDescriptor.getClassFromSerializationPackage(SerialEntityNames.KSERIALIZER_CLASS)
         assert(serializableDescriptor.declaredTypeParameters.size == typeParameters.size)
-        val args = serializableDescriptor.declaredTypeParameters.mapIndexed { index, param ->
-
-            val pType =
-                KotlinTypeFactory.simpleNotNullType(
-                    Annotations.EMPTY,
-                    serializerClass,
-                    listOf(TypeProjectionImpl(typeParameters[index].defaultType))
-                )
+        val args = List(serializableDescriptor.declaredTypeParameters.size) { index ->
+            val pType = KotlinTypeFactory.simpleNotNullType(
+                Annotations.EMPTY,
+                serializerClass,
+                listOf(TypeProjectionImpl(typeParameters[index].defaultType))
+            )
 
             ValueParameterDescriptorImpl(
                 constrDesc, null, index, Annotations.EMPTY, Name.identifier("$typeArgPrefix$index"), pType,