Hello, there. Run into the problem with DISTINCT expression. It works incorrectly on the main query if it was already applied to one of the subqueries bond with UNION ALL.

**How to reproduce**
Server version: 20.5.4.40. 19.17.6.36 was free of the bug.
Using Datagrip for running queries.
Non-default settings:
```
input_format_defaults_for_omitted_fields: 1
decimal_check_overflow: 0
joined_subquery_requires_alias: 0
```

Consider following query
```
select distinct number
from ((select number from numbers(10)) union all (select number from numbers(20)));
```
It works fine, returning 20 rows as expected.

But if we add distinct to subqueries (it doesn't matter to the first, the second or both)
```
select distinct number
from ((select distinct number from numbers(10)) union all (select distinct number from numbers(20)));
```

Then in 20.5.4.40 we'll see 30 rows with numbers from 0 to 9 duplicated.
However, `count(distinct number)` returns the correct number of rows.

{
    const auto & order_by = select_query->orderBy();
    if (!order_by)
        return;
    std::unordered_set<String> prev_keys;
    ASTs modified;
    modified.reserve(order_by->children.size());
    for (auto & order_by_element : order_by->children)
    {
        
        ASTPtr & name_or_function = order_by_element->children[0];
        if (name_or_function->as<ASTFunction>())
        {
            if (!prev_keys.empty())
            {
                RedundantFunctionsInOrderByVisitor::Data data{prev_keys, context};
                RedundantFunctionsInOrderByVisitor(data).visit(name_or_function);
                if (data.redundant)
                    continue;
            }
        }
        
        if (auto * identifier = name_or_function->as<ASTIdentifier>())
            prev_keys.emplace(getIdentifierName(identifier));
        modified.push_back(order_by_element);
    }
    if (modified.size() < order_by->children.size())
        order_by->children = std::move(modified);
}
void optimizeLimitBy(const ASTSelectQuery * select_query)