Avoid duplicate repos/deps/imports in the smithy-build.json

[daddykotex]

Already happening in mill https://github.com/disneystreaming/smithy4s/blob/series/0.18/modules/mill-codegen-plugin/src/smithy4s/codegen/LSP.scala#L47

PR Checklist (not all items are relevant to all PRs)

• Added unit-tests (for runtime code)
• Added bootstrapped code + smoke tests (when the rendering logic is modified)
• Added build-plugins integration tests (when reflection loading is required at codegen-time)
• Added alloy compliance tests (when simpleRestJson protocol behaviour is expanded/updated)
• Updated dynamic module to match generated-code behaviour
• Added documentation
• Updated changelog