[IR] Move Ir utils from Kotlin/Native

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/ir/IrBuilder.kt

@@ -253,12 +253,4 @@ object JsIrBuilder {
     fun buildString(type: IrType, s: String) = IrConstImpl.string(UNDEFINED_OFFSET, UNDEFINED_OFFSET, type, s)
     fun buildTry(type: IrType) = IrTryImpl(UNDEFINED_OFFSET, UNDEFINED_OFFSET, type)
     fun buildCatch(ex: IrVariable, block: IrBlockImpl) = IrCatchImpl(UNDEFINED_OFFSET, UNDEFINED_OFFSET, ex, block)
-}
-
-fun IrClass.simpleFunctions(): List<IrSimpleFunction> = this.declarations.flatMap {
-    when (it) {
-        is IrSimpleFunction -> listOf(it)
-        is IrProperty -> listOfNotNull(it.getter, it.setter)
-        else -> emptyList()
-    }
 }