Remove unused buildIterator import. (Kotlin#3344)

This function has been deprecated for a while.

Author: mpetrov

kotlinx-coroutines-core/jvm/test/internal/LockFreeLinkedListLongStressTest.kt

@@ -9,7 +9,6 @@ import org.junit.Test
 import java.util.*
 import java.util.concurrent.atomic.AtomicInteger
 import kotlin.concurrent.thread
-import kotlin.sequences.buildIterator
 
 /**
  * This stress test has 2 threads adding on one side on list, 2 more threads adding on the other,