dillon1000/react

Removed test support for medikoo/es6-symbol

There seems to be a bug with medikoo/es6-symbol where the global state
affects the implementation of the polyfill. I found this by running the
individual test file alone then running all the tests using `grunt
test`. I found that it passes when ran alone and failed when ran
collectively.

I did not find this buggy behavior with zloirock/core-js's
implementation of a polyfill for Symbol. Thus, removing I will keep the
more popular polyfill (core-js) and remove the buggy polyfill
(es6-symbol).

If you are reading this and can think of a confounding factor that is
causing this bug, please let me know and we can try to work together to
add support for medikoo/es6-symbol.