nixos/pantheon: Replace sessionCommands with extraInit

I think the issue here will be similar to issue 276028.

Author: bobby285271

nixos/modules/services/x11/desktop-managers/pantheon.nix

@@ -112,20 +112,17 @@ in
       # https://github.com/elementary/greeter/issues/368
       services.displayManager.defaultSession = mkDefault "pantheon";
 
-      services.xserver.displayManager.sessionCommands = ''
-        if test "$XDG_CURRENT_DESKTOP" = "Pantheon"; then
-            true
-            ${concatMapStrings (p: ''
-              if [ -d "${p}/share/gsettings-schemas/${p.name}" ]; then
-                export XDG_DATA_DIRS=$XDG_DATA_DIRS''${XDG_DATA_DIRS:+:}${p}/share/gsettings-schemas/${p.name}
-              fi
-
-              if [ -d "${p}/lib/girepository-1.0" ]; then
-                export GI_TYPELIB_PATH=$GI_TYPELIB_PATH''${GI_TYPELIB_PATH:+:}${p}/lib/girepository-1.0
-                export LD_LIBRARY_PATH=$LD_LIBRARY_PATH''${LD_LIBRARY_PATH:+:}${p}/lib
-              fi
-            '') cfg.sessionPath}
-        fi
+      environment.extraInit = ''
+        ${concatMapStrings (p: ''
+          if [ -d "${p}/share/gsettings-schemas/${p.name}" ]; then
+            export XDG_DATA_DIRS=$XDG_DATA_DIRS''${XDG_DATA_DIRS:+:}${p}/share/gsettings-schemas/${p.name}
+          fi
+
+          if [ -d "${p}/lib/girepository-1.0" ]; then
+            export GI_TYPELIB_PATH=$GI_TYPELIB_PATH''${GI_TYPELIB_PATH:+:}${p}/lib/girepository-1.0
+            export LD_LIBRARY_PATH=$LD_LIBRARY_PATH''${LD_LIBRARY_PATH:+:}${p}/lib
+          fi
+        '') cfg.sessionPath}
       '';
 
       # Default services