xo-reader: refactor: use parsestatemachine w/ on_symbol_token()

src/reader/exprseq_xs.cpp

@@ -42,8 +42,7 @@ namespace xo {
 
         void
         exprseq_xs::on_symbol_token(const token_type & tk,
-                                    exprstatestack * /*p_stack*/,
-                                    rp<Expression> * /*p_emit_expr*/)
+                                    parserstatemachine * /*p_psm*/)
         {
             constexpr const char * c_self_name = "exprseq_xs::on_symbol_token";