Remove IrClass.isFileClass as unneeded

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrClass.kt

@@ -35,7 +35,6 @@ interface IrClass : IrSymbolDeclaration<IrClassSymbol>, IrDeclarationWithVisibil
     val isData: Boolean
     val isExternal: Boolean
     val isInline: Boolean
-    val isFileClass: Boolean
 
     val superTypes: MutableList<IrType>
 

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrClassImpl.kt

@@ -44,8 +44,7 @@ class IrClassImpl(
     override val isInner: Boolean,
     override val isData: Boolean,
     override val isExternal: Boolean,
-    override val isInline: Boolean,
-    override val isFileClass: Boolean = false
+    override val isInline: Boolean
 ) :
     IrDeclarationBase(startOffset, endOffset, origin),
     IrClass {

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyClass.kt

@@ -66,8 +66,6 @@ class IrLazyClass(
         symbol.bind(this)
     }
 
-    override val isFileClass = false // file classes are never crated lazily
-
     override val annotations: MutableList<IrCall> = arrayListOf()
 
     override val descriptor: ClassDescriptor get() = symbol.descriptor