Also removes the toolchain builds from flake.nix. For now the flake
build uses upstream Go 1.20, a followup change will switch it back to
our custom toolchain.
Updates tailscale/corp#9005
Signed-off-by: David Anderson <danderson@tailscale.com>
With this, you can import "github:tailscale/tailscale" as a nix flake,
and get access to the "tailscale-unstable" package.
Updates #6845.
Signed-off-by: David Anderson <dave@natulte.net>
