Merge boxWithStdlib testData into box, delete BoxWithStdlib test

compiler/testData/codegen/box/regressions/Kt1619Test.kt

@@ -0,0 +1,19 @@
+// WITH_RUNTIME
+
+package regressions
+
+class Kt1619Test {
+
+    fun doSomething(list: List<String?>): Int {
+        return list.size
+    }
+
+    fun testCollectionNotNullCanBeUsedForNullables(): Int {
+        val list: List<String> = arrayListOf("foo", "bar")
+        return doSomething(list)
+    }
+}
+
+fun box(): String {
+   return if (Kt1619Test().testCollectionNotNullCanBeUsedForNullables() == 2) "OK" else "fail"
+}