[JS] Remove non-functional IGNORE_FIR directive in js box tests

js/js.translator/testData/box/incremental/clashingPrivateDeclarations.kt

@@ -1,4 +1,3 @@
-// IGNORE_FIR
 // NO_COMMON_FILES
 // MODULE: lib
 // FILE: lib.kt
@@ -23,4 +22,4 @@ fun box(): String {
     if (testLib() != "Lib") return "fail1"
     if (testAux() != "Aux") return "fail2"
     return ok()
-}
+}