Use new sequence builders in tests

Coroutine tests will fail when LV=1.2 because there're no such builders
in kotlin.coroutines.experimental.

#KT-26678

compiler/testData/codegen/bytecodeText/coroutines/debug/localVariableCorrectLabel.kt

@@ -1,10 +1,9 @@
 // LANGUAGE_VERSION: 1.3
 
-import kotlin.coroutines.*
 import kotlin.sequences.*
 
 fun main(args: Array<String>) {
-    val s = buildSequence {
+    val s = sequence {
         yield(1)
         val a = awaitSeq()
         println(a) // (1)
@@ -12,7 +11,7 @@ fun main(args: Array<String>) {
     println(s.toList())
 }
 
-suspend fun SequenceBuilder<Int>.awaitSeq(): Int = 42
+suspend fun SequenceScope<Int>.awaitSeq(): Int = 42
 
 // 1 LOCALVARIABLE a I L18 L22 3
-// 1 LINENUMBER 10 L18
+// 1 LINENUMBER 9 L18