Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/extensionFunctions/kt1249.kt

@@ -0,0 +1,12 @@
+//KT-1249 IllegalStateException invoking function property
+class TestClass(val body : () -> Unit) : Any() {
+    fun run() {
+        body()
+    }
+}
+
+fun box() : String {
+    TestClass({}).run()
+    return "OK"
+}
+