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/twoParentsWithTheSameMethodOneBridge.kt

@@ -0,0 +1,22 @@
+trait A<T> {
+    fun foo(t: T) = "A"
+}
+
+trait B<T> {
+    fun foo(t: T) = "B"
+}
+
+class Z : A<Int>, B<Int> {
+    override fun foo(t: Int) = "Z"
+}
+
+
+fun box(): String {
+    val z = Z()
+    return when {
+        z.foo(0)            != "Z" -> "Fail #1"
+        (z : A<Int>).foo(0) != "Z" -> "Fail #2"
+        (z : B<Int>).foo(0) != "Z" -> "Fail #3"
+        else -> "OK"
+    }
+}