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/string-prototype-split.js

@@ -149,3 +149,13 @@ catch (e)
   assert (e instanceof ReferenceError);
   assert (e.message === "foo");
 }
+
+var str = "foo//bar/baz//foo";
+res = str.split("a", Infinity);
+assert (res.length === 0);
+
+res = str.split(/\/\//, -1);
+assert (res.length === 3);
+assert (res[0] === "foo");
+assert (res[1] === "bar/baz");
+assert (res[2] === "foo");