…ndency on zend-filter

…tests to provide coverage

When mbstrings extension is not present the filter has different output behaviour. The behaviour difference is a
degradation rather than a break. Ie when an underscore proceeds a unicode lower case character it will leave that
character pair alone. And when A camel cased character is unicode it will separate it with an underscore but leave
the unicode character upper case. These changed behaviours leave extract/hydrate functional in both directions.

A test asset contained input filter usage but in unused code path. So I removed it which frees us from the require-dev zend-inputfilter dependency