Move blackBoxFile() testData to box/ directory

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

compiler/testData/codegen/box/controlStructures/kt3203_1.kt

@@ -0,0 +1,19 @@
+fun testIf() {
+    val condition = true
+    val result = if (condition) {
+        val hello: String? = "hello"
+        if (hello == null) {
+            false
+        }
+        else {
+            true
+        }
+    }
+    else true
+    if (!result) throw AssertionError("result is false")
+}
+
+fun box(): String {
+    testIf()
+    return "OK"
+}