gnulib-tool: Remove all *.Po files upon distclean (regr. 2022-01-05). Reported by Mohammad Akhlaghi <mohammad@akhlaghi.org> in <https://lists.gnu.org/archive/html/bug-gnulib/2022-01/msg00061.html>. * gnulib-tool (func_emit_initmacro_end): Collect the *.Po or *.Plo files to remove into an AC_SUBSTed variable gl_LIBOBJDEPS. (func_emit_lib_Makefile_am): Extend the distclean and maintainer-clean rules.