[JS IR] Remove unused CALLABLE_CLOSURE_DECLARATION declaration origin

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

@@ -147,8 +147,6 @@ class JsIrBackendContext(
         // TODO: due to name clash those weird suffix is required, remove it once `MemberNameGenerator` is implemented
         private val COROUTINE_SUSPEND_OR_RETURN_JS_NAME = "suspendCoroutineUninterceptedOrReturnJS"
         private val GET_COROUTINE_CONTEXT_NAME = "getCoroutineContext"
-
-        val callableClosureOrigin = object : IrDeclarationOriginImpl("CALLABLE_CLOSURE_DECLARATION") {}
     }
 
     private val internalPackage = module.getPackage(JS_PACKAGE_FQNAME)

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/IrElementToJsStatementTransformer.kt

@@ -27,10 +27,8 @@ import org.jetbrains.kotlin.js.backend.ast.*
 @Suppress("PARAMETER_NAME_CHANGED_ON_OVERRIDE")
 class IrElementToJsStatementTransformer : BaseIrElementToJsNodeTransformer<JsStatement, JsGenerationContext> {
 
-    override fun visitFunction(declaration: IrFunction, data: JsGenerationContext) = JsEmpty.also {
-        assert(declaration.origin == JsIrBackendContext.callableClosureOrigin) {
-            "The only possible Function Declaration is one composed in Callable Reference Lowering"
-        }
+    override fun visitFunction(declaration: IrFunction, data: JsGenerationContext): JsStatement {
+        error("All functions must be already lowered")
     }
 
     override fun visitBlockBody(body: IrBlockBody, context: JsGenerationContext): JsStatement {