Remove redundant Validator test

If for some reason `$this->validator` doesn't exist, all the other tests
will fail. This test wasn't really doing anything, other than asserting
our test setup was correct, so let's just remove it.

spec/dependencies/validator.spec.php

@@ -15,10 +15,6 @@
 		);
 	});
 
-	it('exists', function () {
-		$this->validator;
-	});
-
 	describe('->validate()', function () {
 		context('whippet.lock cannot be found, or is invalid JSON', function () {
 			it('returns an error', function () {