Add more tests for JsonObjectConst

extras/tests/JsonObject/containsKey.cpp

@@ -15,12 +15,6 @@ TEST_CASE("JsonObject::containsKey()") {
     REQUIRE(true == obj.containsKey("hello"));
   }
 
-  SECTION("works with JsonObjectConst") {
-    JsonObjectConst cobj = obj;
-    REQUIRE(false == cobj.containsKey("world"));
-    REQUIRE(true == cobj.containsKey("hello"));
-  }
-
   SECTION("returns false after remove()") {
     obj.remove("hello");