When not empty, AT_PARSE_PARAMS was guaranteed to end with a comma.
Remove the trailing comma, so that we can use AT_PARSE_PARAMS at the
end of the arguments, not only at the beginning.
* tests/local.at: here.
Unfortunately, m4_append relies on the macro not being defined whereas
we would have preferred it to check for emptiness. So use
m4_define/m4_undefine instead of m4_pushdef/m4_popdef.
ece99a890c