Remove nightly from zed1 and use proper namespaces for nightly in zed2 manifest (#3745)

Currently, I get 404 when trying to open links for nightly, like
https://zed.dev/nightly/channel/Rooms-329
The PR ensures nightly has a separate protocol handler in zed2, removes
nightly mentions from zed1.

See also zed.dev change:
https://github.com/zed-industries/zed.dev/pull/429

Release Notes:

- N/A
8238edb5aaKirill Bulatov committed on 12/20/2023, 11:24:57 PM· committed by GitHubparents56f2b962cd7d2d
2 files changedLine totals unavailable