fix(nix): don't wait for multi-user.target

in the `anything-sync-daemon` Nix flake check, as it (a) appears to be
unnecessary to do so (even though we need an `asduser` session to run
certain assertions) and (b) appears to break the check on GitHub
actions, as we hit the retry timeout before `multi-user.target` is
reached.

Author: tomeon

nix/checks.nix

@@ -33,8 +33,6 @@
             asd.start_job('asd.service')
             asd.wait_for_unit('asd.service')
 
-          asd.wait_for_unit('multi-user.target')
-
           # Ensure user session doesn't end when user logs out
           asd.succeed("loginctl enable-linger ${user}")