When Tailscale is installed via Homebrew, `/usr/local/bin/tailscaled`
is a symlink to the actual binary.
Now when `tailscaled install-system-daemon` runs, it will not attempt
to overwrite that symlink if it already points to the tailscaled binary.
However, if executed binary and the link target differ, the path will
he overwritten - this can happen when a user decides to replace
Homebrew-installed tailscaled with a one compiled from source code.
Fixes#5353
Signed-off-by: Anton Tolchanov <anton@tailscale.com>
c070d39287