stage-2 init: move /run/keys mount to boot.specialFileSystems

nixos/modules/system/boot/stage-2-init.sh

@@ -111,16 +111,6 @@ rm -f /etc/{group,passwd,shadow}.lock
 rm -rf /nix/var/nix/gcroots/tmp /nix/var/nix/temproots
 
 
-# Create a ramfs on /run/keys to hold secrets that shouldn't be
-# written to disk (generally used for NixOps, harmless elsewhere).
-if ! mountpoint -q /run/keys; then
-    rm -rf /run/keys
-    mkdir /run/keys
-    mount -t ramfs ramfs /run/keys
-    chown 0:96 /run/keys
-    chmod 0750 /run/keys
-fi
-
 mkdir -m 0755 -p /run/lock