Revert "sshAuthSock: assert that at most one agent is enabled"

This reverts commit 9dc93220c1.

On one hand, conflicting definitions for `sshAuthSock.initialization.*`
were triggering before the assertion triggered, hereby making the
assertion redundant. On the other hand, the assertion prevents users
from running multiple agents side-by-side even after resolving the
definition conflict.

See https://github.com/nix-community/home-manager/pull/8533#issuecomment-4224165151.

modules/misc/ssh-auth-sock.nix

@@ -63,38 +63,11 @@ in
     type = with lib.types; nullOr (submodule initSubmodule);
   };
 
-  config = lib.mkMerge [
-    {
-      assertions = [
-        {
-          assertion =
-            lib.count (x: x) [
-              (config.services.ssh-agent.enable || config.services.ssh-tpm-agent.enable)
-              (config.services.gpg-agent.enable && config.services.gpg-agent.enableSshSupport)
-              config.services.proton-pass-agent.enable
-              config.services.yubikey-agent.enable
-            ] <= 1;
-          message = ''
-            Out of the SSH agents
-
-            - ssh-agent or ssh-tpm-agent (these two can coexist),
-            - gpg-agent with SSH support enabled, and
-            - proton-pass-agent,
-            - yubikey-agent,
-
-            at most one of them may be enabled (with the exception of ssh-agent and
-            ssh-tpm-agent).
-          '';
-        }
-      ];
-    }
-
-    (lib.mkIf (cfg.initialization != null) {
-      # $SSH_AUTH_SOCK has to be set early since other tools rely on it
-      programs.bash.profileExtra = lib.mkOrder 900 bashIntegration;
-      programs.fish.shellInit = lib.mkOrder 900 fishIntegration;
-      programs.nushell.extraConfig = lib.mkOrder 900 nushellIntegration;
-      programs.zsh.envExtra = lib.mkOrder 900 bashIntegration;
-    })
-  ];
+  config = lib.mkIf (cfg.initialization != null) {
+    # $SSH_AUTH_SOCK has to be set early since other tools rely on it
+    programs.bash.profileExtra = lib.mkOrder 900 bashIntegration;
+    programs.fish.shellInit = lib.mkOrder 900 fishIntegration;
+    programs.nushell.extraConfig = lib.mkOrder 900 nushellIntegration;
+    programs.zsh.envExtra = lib.mkOrder 900 bashIntegration;
+  };
 }

tests/modules/misc/ssh-auth-sock/conflicts.nix

@@ -1,21 +0,0 @@
-{
-  services.gpg-agent = {
-    enable = true;
-    enableSshSupport = true;
-  };
-  services.ssh-agent.enable = true;
-
-  test.asserts.assertions.expected = [
-    ''
-      Out of the SSH agents
-
-      - ssh-agent or ssh-tpm-agent (these two can coexist),
-      - gpg-agent with SSH support enabled, and
-      - proton-pass-agent,
-      - yubikey-agent,
-
-      at most one of them may be enabled (with the exception of ssh-agent and
-      ssh-tpm-agent).
-    ''
-  ];
-}

tests/modules/misc/ssh-auth-sock/default.nix

@@ -1,4 +1,3 @@
 {
-  sshAuthSock-conflicts = ./conflicts.nix;
   sshAuthSock-initialization = ./initialization.nix;
 }