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/innerExtentionFunctionDouble.kt

@@ -0,0 +1,15 @@
+class A {
+  fun Double.foo(a: Double = 1.0): Double {
+      return a
+  }
+
+  fun test(): String {
+      if (1.0.foo() != 1.0) return "fail"
+      if (1.0.foo(2.0) != 2.0) return "fail"
+      return "OK"
+  }
+}
+
+fun box(): String  {
+   return A().test()
+}