[JS IR BE] Fix and refactor interop tests

js/js.translator/testData/box/jsName/privateMethod.kt

@@ -1,13 +1,12 @@
 // IGNORE_BACKEND: JS_IR
 // EXPECTED_REACHABLE_NODES: 1290
-package foo
 
 object A {
     @JsName("js_f") private fun f(x: Int) = "f($x)"
 }
 
 fun test() = js("""
-return JS_TESTS.foo.A.js_f(23);
+return JS_TESTS.A.js_f(23);
 """)
 
 fun box(): String {