modules: secrets: move non-existent key workaround

Since this configuration was only there to accommodate `aramis`, make it
be host-specific instead, and rely on the default value otherwise.

hosts/nixos/aramis/secrets/default.nix

@@ -16,5 +16,10 @@
         secrets = import ./secrets.nix;
       in
       lib.mapAttrs' convertSecrets secrets;
+
+    identityPaths = [
+      # Due to being a laptop, this host does not itself have any SSH keys
+      "/home/ambroisie/.ssh/id_ed25519"
+    ];
   };
 }

modules/secrets/default.nix

@@ -20,10 +20,5 @@
         secrets = import ./secrets.nix;
       in
       lib.mapAttrs' convertSecrets secrets;
-
-    identityPaths = options.age.identityPaths.default ++ [
-      # FIXME: hard-coded path, could be inexistent
-      "/home/ambroisie/.ssh/id_ed25519"
-    ];
   };
 }