Move simplification to `rs merge` pipeline step

[daniel-j-h]

Currently in rs feature we extract polygons and simplify them. Then in rs merge we buffer, then union, then unbuffer for merging shapes across tile boundaries. This leads to polygons that are no longer simplified.

We should investigate not simplifying in rs feature. Instead merge un-simplified geometries, then simplify in rs merge at the end of the pipeline.

Tasks:

• [ ] Remove simplification in rs feature
• [ ] Implement simplification in rs merge after merging shapes