Remove whitespace variables from .dir-locals.el

The overriding whitespace-style had the annoying effect of hiding tabs
in whitespace-mode. Furthermore, when testing with emacs -Q, it was
triggering the unsafe local variable warning.

To compensate for removing whitespace handling from emacs, add a
whitespace check into the travis test.

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I hope it's okay to get rid of these? It's really been annoying me for a while now.