toke.c: Rewrite bogus yylex comment

toke.c: Rewrite bogus yylex comment

This comment has been wrong since it was first added.  What it des-
cribed was then the code at the beginning of yylex, before the main
tokenizing switch.

Since then, two parts of what it described have moved elsewhere; the
pending identifier code to S_pending_ident, and the sort $a<=>$b check
to op.c:S_simplify_sort.