StdLib cleanup: remove unused imports

libraries/stdlib/test/io/Files.kt

@@ -8,9 +8,7 @@ import java.util.HashSet
 import java.util.ArrayList
 import kotlin.io.walkBottomUp
 import kotlin.io.walkTopDown
-import kotlin.test.assertFalse
-import kotlin.test.assertNull
-import kotlin.test.assertTrue
+import kotlin.test.*
 
 class FilesTest {
 

libraries/stdlib/test/io/IOStreams.kt

@@ -4,7 +4,6 @@ import org.junit.Test as test
 import kotlin.test.*
 import java.io.Writer
 import java.io.BufferedReader
-import java.io.File
 
 class IOStreamsTest {
     @test fun testGetStreamOfFile() {