[FIR generator] Deduplicate the logic of needPureAbstractElement

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/implementation.kt

@@ -98,7 +98,7 @@ fun SmartPrinter.printImplementation(implementation: Implementation) {
         }
 
         print(" : ")
-        if (!isInterface && !allParents.any { it.kind == ImplementationKind.AbstractClass || it.kind == ImplementationKind.SealedClass }) {
+        if (needPureAbstractElement) {
             print("${pureAbstractElementType.type}(), ")
         }
         print(allParents.joinToString { "${it.typeWithArguments}${it.kind.braces()}" })

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/utils.kt

@@ -113,10 +113,6 @@ private fun List<String>.filterRedundantImports(
 }
 
 
-val ImplementationKindOwner.needPureAbstractElement: Boolean
-    get() = (kind != ImplementationKind.Interface && kind != ImplementationKind.SealedInterface) && !allParents.any { it.kind == ImplementationKind.AbstractClass || it.kind == ImplementationKind.SealedClass }
-
-
 val Field.isVal: Boolean
     get() = (this is FieldList && !isMutableOrEmpty) || (this is FieldWithDefault && origin is FieldList && !origin.isMutableOrEmpty) || !isMutable