Remove empty queue conditional from slicing logic (#114513)

With recent changes in Lucene around not forking execution when not necessary, we have
removed the search worker thread pool in #111099. The worker thread pool had unlimited queue,
and the fear was that we couuld have much more queueing on the search thread pool if we use
it to parallelize execution across segments, because every shard would take up to a thread
per slice when executing the query phase.

We have then introduced an additional conditional to stop parallelizing when there is a queue.
That is perhaps a bit extreme, as it's a decision made when creating the searcher, while a
queue may no longer be there once the search is executing. This has caused some benchmarks
regressions, hence this commit removes the additional queue dependent conditional in order
to perform additional benchmarks without it.

Author: javanna

server/src/main/java/org/elasticsearch/search/DefaultSearchContext.java

@@ -291,7 +291,6 @@ static int determineMaximumNumberOfSlices(
         ToLongFunction<String> fieldCardinality
     ) {
         return executor instanceof ThreadPoolExecutor tpe
-            && tpe.getQueue().isEmpty()
             && isParallelCollectionSupportedForResults(resultsType, request.source(), fieldCardinality, enableQueryPhaseParallelCollection)
                 ? tpe.getMaximumPoolSize()
                 : 1;