tailscale: drop the 1.98.9 vendorHash override

c5a231b pinned the hash by hand because nixpkgs bumped 1.98.8->1.98.9 without
updating vendorHash (NixOS/nixpkgs#545860). The previous commit's lock moves
nixos-26.05 past the point where that fix was promoted from release-26.05, so
the override is now dead weight — and a stale vendorHash override is worse
than none, since it silently wins over a correct upstream value on the next
version bump.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

services/vpn/tailscale.nix

@@ -5,19 +5,6 @@
 # to declare `sops.secrets.tailscale_authkey` (see each host's secrets.nix).
 # Not for the VM (no sops).
 {
-  # TEMPORARY: nixpkgs bumped tailscale 1.98.8->1.98.9 without updating
-  # vendorHash (NixOS/nixpkgs#545860, fixed on the `release-26.05` branch
-  # 2026-07-26 but not yet promoted to the `nixos-26.05` channel branch this
-  # flake tracks). Remove this override once `nix flake lock --update-input
-  # nixpkgs` picks up a nixos-26.05 rev at/after that fix.
-  nixpkgs.overlays = [
-    (final: prev: {
-      tailscale = prev.tailscale.overrideAttrs (old: {
-        vendorHash = "sha256-Sd2iLJ7eDfDYdIRuW4xuiKgzhQWJWGAnz97FJWrVRlE=";
-      });
-    })
-  ];
-
   services.tailscale = {
     enable = true;
     openFirewall = true;                       # UDP 41641 for direct connections