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/jerry/test_suite_15.js

@@ -2460,3 +2460,9 @@
   var a = new Array(1, 2, 5);
   assert(a.length === 3);
 })();
+
+(function tc_15_03_04_02__001() {
+  assert(Function.prototype.toString.hasOwnProperty('length'));
+  assert(delete Function.prototype.toString.length);
+  assert(!Function.prototype.toString.hasOwnProperty('length'));
+})();