Generate classes in MultifileClassCodegen exactly the same as in PackageCodegen

Two known issues with generateNonPartClassDeclarations that was here
before were the fact that we didn't sort sealed classes and its
subclasses which led to NoSuchMethodError (KT-27097), and the fact that
we didn't skip expect classes which led to incorrect duplicate JVM class
name diagnostic (KT-30843)

 #KT-27097 Fixed
 #KT-30843 Fixed

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

@@ -18,11 +18,9 @@ package org.jetbrains.kotlin.backend.jvm
 
 import org.jetbrains.kotlin.backend.common.phaser.PhaseConfig
 import org.jetbrains.kotlin.codegen.*
-import org.jetbrains.kotlin.codegen.context.PackageContext
 import org.jetbrains.kotlin.codegen.state.GenerationState
 import org.jetbrains.kotlin.descriptors.PackageFragmentDescriptor
 import org.jetbrains.kotlin.name.FqName
-import org.jetbrains.kotlin.psi.KtClassOrObject
 import org.jetbrains.kotlin.psi.KtFile
 import org.jetbrains.kotlin.psi2ir.Psi2IrTranslator
 
@@ -45,10 +43,6 @@ class JvmIrCodegenFactory(private val phaseConfig: PhaseConfig) : CodegenFactory
                 JvmBackendFacade.doGenerateFiles(files, state, errorHandler, phaseConfig)
             }
 
-            override fun generateClassOrObject(classOrObject: KtClassOrObject, packagePartContext: PackageContext) {
-                TODO()
-            }
-
             override fun getPackageFragment(): PackageFragmentDescriptor {
                 return impl.packageFragment
             }