Refactor unnecessary filter-type checks

[sfendrich]

TagKeyBasedOsmElementsFilter comes with filter types AcceptMatching and RemoveMatching. Function accept_by_tags checks for this type on each processed element. This check can be done once, when constructing the filter, e.g., by providing two struct implementations TagKeyBasedAcceptFilter and TagKeyBasedRemoveFilter.

[sfendrich]

So far, these filters are only used in tests, i.e., there is no urge to improve this.