Do not reference java.util in tests that run on JS backend.

compiler/testData/codegen/box/delegatedProperty/local/kt13557.kt

@@ -1,6 +1,5 @@
 //WITH_REFLECT
 
-import java.util.*
 import kotlin.properties.Delegates
 
 fun box(): String {

compiler/testData/codegen/box/delegatedProperty/useKPropertyLater.kt

@@ -1,7 +1,6 @@
 // WITH_REFLECT
 // TODO: replace with WITH_RUNTIME once KT-11316 is fixed
 
-import java.util.*
 import kotlin.reflect.*
 
 val properties = HashSet<KProperty<*>>()