[FIR2IR] Don't use descriptor manglers in FIR2IR

They don't do anything, only complicate the initial configuration.

KT-64990

native/native.tests/tests/org/jetbrains/kotlin/konan/test/ClassicFrontend2NativeIrConverter.kt

@@ -133,7 +133,7 @@ class ClassicFrontend2NativeIrConverter(
             moduleFragment,
             pluginContext,
             diagnosticReporter = DiagnosticReporterFactory.createReporter(),
-            descriptorMangler = (pluginContext.symbolTable as SymbolTable).signaturer.mangler,
+            descriptorMangler = (pluginContext.symbolTable as SymbolTable).signaturer!!.mangler,
             irMangler = KonanManglerIr,
             firMangler = null,
         )

native/native.tests/tests/org/jetbrains/kotlin/konan/test/Fir2IrNativeResultsConverter.kt

@@ -7,7 +7,6 @@ package org.jetbrains.kotlin.konan.test
 
 import org.jetbrains.kotlin.KtSourceFile
 import org.jetbrains.kotlin.backend.common.serialization.metadata.DynamicTypeDeserializer
-import org.jetbrains.kotlin.backend.konan.serialization.KonanManglerDesc
 import org.jetbrains.kotlin.backend.konan.serialization.KonanManglerIr
 import org.jetbrains.kotlin.builtins.konan.KonanBuiltIns
 import org.jetbrains.kotlin.config.CompilerConfiguration
@@ -30,10 +29,6 @@ import org.jetbrains.kotlin.test.services.TestServices
 
 class Fir2IrNativeResultsConverter(testServices: TestServices) : AbstractFir2IrNonJvmResultsConverter(testServices) {
 
-    override fun createDescriptorMangler(): KotlinMangler.DescriptorMangler {
-        return KonanManglerDesc
-    }
-
     override fun createIrMangler(): KotlinMangler.IrMangler {
         return KonanManglerIr
     }
@@ -62,7 +57,7 @@ class Fir2IrNativeResultsConverter(testServices: TestServices) : AbstractFir2IrN
             fir2IrResult.irModuleFragment,
             fir2IrResult.pluginContext,
             diagnosticReporter = diagnosticReporter,
-            descriptorMangler = manglers.descriptorMangler,
+            descriptorMangler = null,
             irMangler = manglers.irMangler,
             firMangler = manglers.firMangler,
         )