[Serialization] Migrate all tests to new test infrastructure

plugins/kotlinx-serialization/testData/boxIr/annotationsOnFile.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // TARGET_BACKEND: JVM_IR
 
 // WITH_STDLIB
@@ -75,4 +74,4 @@ fun testOnFile(): String {
 
 fun box(): String {
     return testOnFile()
-}
+}