Remove generated codegen tests, move all testData to box/

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

compiler/testData/codegen/box/defaultArguments/function/innerExtentionFunctionDoubleTwoArgs.kt

@@ -0,0 +1,17 @@
+class A {
+    fun Double.foo(a: Double = 1.0, b: Double = 1.0): Double {
+        return a + b
+    }
+
+    fun test(): String {
+        if (1.0.foo() != 2.0) return "fail"
+        if (1.0.foo(2.0, 2.0) != 4.0) return "fail"
+        if (1.0.foo(a = 2.0) != 3.0) return "fail"
+        if (1.0.foo(b = 2.0) != 3.0) return "fail"
+        return "OK"
+    }
+}
+
+fun box(): String  {
+    return A().test()
+}