x11/xfce4-appmenu-plugin: drop duplicate localization

po/meson.build:1:5: ERROR: Tried to create target "vala-panel-appmenu-nb.mo", but a target of that name already exists.

https://gitlab.com/vala-panel-project/vala-panel-appmenu/-/commit/442bcebcc00e

PR: 259080
Reported by: antoine (via exp-run)
Regressed by: https://github.com/mesonbuild/meson/commit/487d45c1e5bf