Remove generated codegen tests, move all testData to box/

A single test file will be generated out of box/ directory

compiler/testData/codegen/box/innerNested/innerLabeledThis.kt

@@ -0,0 +1,11 @@
+class Outer {
+    inner class Inner {
+        fun O() = this@Outer.O
+        val K = this@Outer.K()
+    }
+    
+    val O = "O"
+    fun K() = "K"
+}
+
+fun box() = Outer().Inner().O() + Outer().Inner().K