ESQL: drop SortAgnostic interface

[bpintea]

This attempts a simplification, dropping an interface: SortAgnostic

• really targets just one rule, PruneRedundantOrderBy (needed due to the current incapacity to execute unbounded sorts; the rule doesn't actually solve the issue, but it does alleviate it in some cases).
• has a contract which is in part inconsistent (STATS and SORT don't need to be in a pattern to have preceding SORTs dropped -- https://github.com/elastic/elasticsearch/pull/132417/files#r2285043073);
• it requires cognitive load when adding new commands: this interface is implemented by all commands, except one (LIMIT).