Removes array_filter callable to use array_filter default behaviour

[TuzBot]

By default array_filter removes any null entries when filtering through an array, which means the callback is not needed.

Than being said, for those that don't know array_filters default behaviour the written code with the callback shows its intent a bit clearer along with the comment.

[coveralls]

Coverage remained the same at 3.061% when pulling f0201f39add1b9870772f608ab64b3afe5cd27ef on TuzBot:master into 75e93bb822619d8ddb8b1843588caa2fad739491 on jamesryanbell:master.