Remove ES_NEXT macro (#4915)

- remove all '#JERRY_ESNEXT' macro
- remove 5.1 build profile, update test runner accordingly (Note: all builtins are turn on by default)
- move tests from tests/jerry/esnext into tests/jerry, concatenate files with same names
- add skiplist to some snapshot tests that were supported only in 5.1
- fix doxygen issues that were hidden before (bc. of es.next macro)

Co-authored-by: Martin Negyokru negyokru@inf.u-szeged.hu
JerryScript-DCO-1.0-Signed-off-by: Adam Szilagyi aszilagy@inf.u-szeged.hu

tests/unit-core/test-newtarget.c

@@ -108,13 +108,6 @@ construct_handler (const jerry_call_info_t *call_info_p, /**< call information *
 int
 main (void)
 {
-  /* Test JERRY_FEATURE_SYMBOL feature as it is a must-have in ES.next */
-  if (!jerry_feature_enabled (JERRY_FEATURE_SYMBOL))
-  {
-    jerry_log (JERRY_LOG_LEVEL_ERROR, "Skipping test, ES.next support is disabled.\n");
-    return 0;
-  }
-
   jerry_init (JERRY_INIT_EMPTY);
 
   jerry_value_t demo_func = register_js_function ("Demo", construct_handler);