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.

vala-panel-project/vala-panel-appmenu@442bcebc

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