Remove redundant test in lex_is_idn().

Remove redundant test in lex_is_idn().

Commit 90f346cc0 "Made var_is_valid_name more permissive" made characters
with values above 127 valid in identifiers by allowing them in
lex_is_id1() and lex_is_idn(), but since the latter includes the former
in its test the addition there is redundant and can be eliminated.