Remove `opt_filter` optional parameter in GroupsAccumulator:merge

That is why I return error for now, we can remove the `opt_filter` after couple of months

_Originally posted by @jayzhan211 in https://github.com/apache/datafusion/pull/13463#discussion_r1847462304_

The idea is that the parameter is never used, so we can remove it to simplify GroupsAccumulator implementations.

@jayzhan211s PRs above throws an error if this assumption is not true.

If we haven't hit any errors in a few months, we should just remove the parameter entirely

Start by searching the Rust codebase for GroupsAccumulator::merge and the opt_filter parameter, then review the implementations and the PR discussion linked in the issue. Confirm that the parameter is unused and that the existing error checks are no longer needed; done means the parameter is removed consistently without triggering the previously guarded errors.

Written by the indexing model from the issue text.