duplicated filter

[matkoniecz]

https://github.com/tangrams/cinnabar-style/blob/gh-pages/cinnabar-style.yaml#L850
https://github.com/tangrams/cinnabar-style/blob/gh-pages/cinnabar-style.yaml#L851

https://github.com/tangrams/cinnabar-style/blob/gh-pages/cinnabar-style.yaml#L888
https://github.com/tangrams/cinnabar-style/blob/gh-pages/cinnabar-style.yaml#L889

first line is completely useless an second has smaller requirement

not sure what is the intended meaning - delete first/second line? Decrement all z-levels from lowest to first duplicated? Increment all from first duplicated to highest?

[matkoniecz]

Also, not sure is it available but filtering by displayed area rather than real area would be probably more readable and less error prone - like at https://github.com/gravitystorm/openstreetmap-carto/blob/master/water.mss#L322