Use kotlin.test.Test instead of org.junit.Test in common stdlib tests

(and in jvm-only and js-only tests also)

libraries/stdlib/test/properties/delegation/DelegationTest.kt

@@ -1,6 +1,5 @@
 package test.properties.delegation
 
-import org.junit.Test
 import kotlin.test.*
 import kotlin.properties.*
 

libraries/stdlib/test/properties/delegation/MapAccessorsTest.kt

@@ -1,7 +1,6 @@
 package test.properties.delegation.map
 
 import kotlin.test.*
-import org.junit.Test
 
 class ValByMapExtensionsTest {
     val map: Map<String, String> = hashMapOf("a" to "all", "b" to "bar", "c" to "code")

libraries/stdlib/test/properties/delegation/lazy/LazyValuesTest.kt

@@ -1,6 +1,5 @@
 package test.properties.delegation.lazy
 
-import org.junit.Test
 import kotlin.properties.*
 import kotlin.test.*