Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/bridges/kt2833.kt

@@ -0,0 +1,17 @@
+package test
+
+public trait FunDependencyEdge {
+    val from: FunctionNode
+}
+
+public trait FunctionNode
+
+public class FunctionNodeImpl : FunctionNode
+
+class FunDependencyEdgeImpl(override val from: FunctionNodeImpl): FunDependencyEdge {
+}
+
+fun box(): String {
+    (FunDependencyEdgeImpl(FunctionNodeImpl()) as FunDependencyEdge).from
+    return "OK"
+}