style(core): drop the comments restating the shuffle-write join order

The reasoning is in the fix commit; the code does not need it repeated.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: Dandandan

ballista/core/src/execution_plans/shuffle_writer.rs

@@ -592,12 +592,6 @@ impl ShuffleWriterExec {
                 });
             }
 
-            // Joined as they complete, not in partition order: the K drains
-            // share one plan instance, so a panic while its `CollectLeft` build
-            // side (DataFusion's `OnceFut`) is polled leaves the others parked
-            // on that future forever — joining in order would block on one of
-            // them and hang the job instead of failing it. Dropping the
-            // `JoinSet` on the way out aborts whatever is still parked.
             let mut results = Vec::with_capacity(num_partitions);
             while let Some(joined) = handles.join_next().await {
                 let (local_input_partition, stats) = joined.map_err(|e| {

ballista/core/src/execution_plans/sort_shuffle/writer.rs

@@ -1063,12 +1063,6 @@ async fn run_coordinator(
     // Spawn per-input-partition write tasks concurrently — this matches the
     // parallelism main's design achieved by having DataFusion drive
     // `execute(0..M)` concurrently.
-    //
-    // Joined as they complete, not in partition order, and the first failure
-    // abandons the rest: the M writes share one plan instance, so a panic while
-    // its `CollectLeft` build side (DataFusion's `OnceFut`) is polled leaves the
-    // others parked on that future forever — joining in order would block on one
-    // of them and hang the job instead of failing it.
     let mut writes = JoinSet::new();
     for input_partition in 0..num_input_partitions {
         let w = writer.clone();