sshd: Always start a session

Partially reverts 70a4c7b1dfdb238d3729c3f71127538943a43afd. Whether to
start a session is independent of whether we're running in a
container.

nixos/modules/services/networking/ssh/sshd.nix

@@ -284,7 +284,7 @@ in
     networking.firewall.allowedTCPPorts = cfg.ports;
 
     security.pam.services.sshd =
-      { startSession = !config.boot.isContainer;
+      { startSession = true;
         showMotd = true;
         unixAuth = cfg.passwordAuthentication;
       };