Variable $enable-rounded doesn't disable border-radius in buttons

Created by: brunnopleffken

I don't know if this is the expected behavior, but in Beta.2 setting $enable-rounded to false doesn't change the border-radius value of .btn classes at all, instead it just left the browser's default value.

Shouldn't BS set it to zero like it does in .form-control? Otherwise I'll have to override CSS classes in my application.css anyway like .btn { border-radius: 0; } and I believe this is not the main BS4 goal.

Thanks!