(0.19) Remove optics settings from build tools

[kubukoz]

https://disneystreaming.github.io/smithy4s/docs/codegen/customisation/optics/

If you're using Smithy4s via mill or sbt, then you can enable this functionality with the following keys:

    in mill, task: def smithy4sRenderOptics = true
    in sbt, setting: smithy4sRenderOptics := true

Citing @Baccata, we don't want to maintain such configuration on the build tool level, it should rather be configurable via Smithy metadata in additional Smithy source files.

In this case, it already is:

metadata smithy4sRenderOptics = true

so it should be a straightforward removal.

This will possibly break existing usage, so it should target the series/0.19 branch.