fix(tazjin/nixos): delete firefox from machines

Quassel sometimes thinks it's a reasonable thing to do to start
firefox instead of my default browser. Why? I've got no clue.

But since I don't use Firefox anyways unless there's a special
situation going on, lets just delete it.

Change-Id: Ib7ad4cc53c44ac47f3a0c3922600c3915f90219c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7646
Autosubmit: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

users/tazjin/nixos/modules/physical.nix

@@ -28,7 +28,6 @@ in
       exa
       fd
       file
-      firefox
       gdb
       gh
       git