Removes a dead `ExternalLinkIcon` constant and its now-orphaned
`ArrowUpRight` import that were breaking the build with a TS6133
(declared but never read) error.
**Removed:**
- `ExternalLinkIcon` constant and the `ArrowUpRight` lucide import
(unused)
## To test
- `pnpm typecheck --filter=studio` passes
- Database menu still renders normally
<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
* **Chores**
* Removed an unused icon import and a redundant internal constant.
* No user-facing behavior or menu options changed.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
Co-authored-by: Alaister Young <10985857+alaister@users.noreply.github.com>
