Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/functions/kt873.kt

@@ -0,0 +1,11 @@
+fun box() : String {
+  val fps  : Double = 1.toDouble()
+  var mspf : Long
+  {
+    if ((fps.toInt() == 0))
+      mspf = 0
+    else
+      mspf = (((1000.0 / fps)).toLong())
+  }
+  return "OK"
+}