Drop isErrorTypeAllowed flag from type system context

The flag was used exclusively during calculation of common super type.
This change relies on assumption, that common super type is
NOT calculated in IR type system context.

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSystemContext.kt

@@ -35,8 +35,6 @@ interface IrTypeSystemContext : TypeSystemContext, TypeSystemCommonSuperTypesCon
 
     val irBuiltIns: IrBuiltIns
 
-    override val isErrorTypeAllowed: Boolean get() = true
-
     override fun KotlinTypeMarker.asSimpleType() = this as? SimpleTypeMarker
 
     override fun KotlinTypeMarker.asFlexibleType() = this as? IrDynamicType

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeUtils.kt

@@ -70,6 +70,8 @@ fun IrType.isSubtypeOf(superType: IrType, irBuiltIns: IrBuiltIns): Boolean {
     return AbstractTypeChecker.isSubtypeOf(IrTypeCheckerContext(irBuiltIns) as AbstractTypeCheckerContext, this, superType)
 }
 
+// no searchable usages
+// delete or FIXME: implement TypeConstructorMarker.isError and TypeConstructorMarker.toErrorType in IrTypeSystemContext
 fun Collection<IrType>.commonSupertype(irBuiltIns: IrBuiltIns): IrType {
     return NewCommonSuperTypeCalculator.run {
         IrTypeCheckerContext(irBuiltIns).commonSuperType(map { it }) as IrType