Remove Flatpak warning now that sandboxing is reverted (#55673)

Self-Review Checklist:

- [ ] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [ ] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [ ] Performance impact has been considered and is acceptable

Closes #ISSUE

Release Notes:

- N/A

docs/src/linux.md

@@ -53,7 +53,7 @@ There are several third-party Zed packages for various Linux distributions and p
 - Parabola: [`zed`](https://www.parabola.nu/packages/extra/x86_64/zed/)
 - ALT Linux (Sisyphus): [`zed`](https://packages.altlinux.org/en/sisyphus/srpms/zed/)
 - AOSC OS: [`zed`](https://packages.aosc.io/packages/zed)
-- Flathub: [`dev.zed.Zed`](https://flathub.org/apps/dev.zed.Zed) (WARNING: [Sandboxing causes problems](https://github.com/flathub/dev.zed.Zed/pull/275))
+- Flathub: [`dev.zed.Zed`](https://flathub.org/apps/dev.zed.Zed)
 
 See [Repology](https://repology.org/project/zed-editor/versions) for a list of Zed packages in various repositories.