JVM_IR. Remove FileClassDescriptor, no longer used

compiler/backend/src/org/jetbrains/kotlin/codegen/OwnerKind.kt

@@ -5,7 +5,6 @@
 
 package org.jetbrains.kotlin.codegen
 
-import org.jetbrains.kotlin.codegen.descriptors.FileClassDescriptor
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
 import org.jetbrains.kotlin.descriptors.PackageFragmentDescriptor
@@ -18,7 +17,7 @@ enum class OwnerKind {
 
     companion object {
         fun getMemberOwnerKind(descriptor: DeclarationDescriptor): OwnerKind = when (descriptor) {
-            is FileClassDescriptor, is PackageFragmentDescriptor -> OwnerKind.PACKAGE
+            is PackageFragmentDescriptor -> OwnerKind.PACKAGE
             is ClassDescriptor -> OwnerKind.IMPLEMENTATION
             else -> throw AssertionError("Unexpected declaration container: $this")
         }

compiler/backend/src/org/jetbrains/kotlin/codegen/descriptors/FileClassDescriptor.kt

@@ -1,21 +0,0 @@
-/*
- * Copyright 2010-2017 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.jetbrains.kotlin.codegen.descriptors
-
-import org.jetbrains.kotlin.descriptors.ClassDescriptor
-
-interface FileClassDescriptor : ClassDescriptor