Move blackBoxFile() testData to box/ directory

Delete all test methods (and empty test classes), since they'll be
auto-generated

compiler/testData/codegen/box/vararg/kt581.kt

@@ -0,0 +1,22 @@
+package whats.the.difference
+
+import java.util.HashSet
+
+fun iarray(vararg a : Int) = a // BUG
+
+fun IntArray.lastIndex() = size - 1
+
+fun box() : String {
+    // Problematic code does not compile
+//    val vals = iarray(789, 678, 567, 456, 345, 234, 123, 012)
+
+    val vals = iarray(789, 678, 567, 456, 345, 234, 123, 12)
+    val diffs = HashSet<Int>()
+    for (i in vals.indices)
+        for (j in i..vals.lastIndex())
+             diffs.add(vals[i] - vals[j])
+    val size = diffs.size()
+
+    if (size != 8) return "Fail $size"
+    return "OK"
+}