Removing dead arg (#24447)

## Description

<#23737> deprecated this arg in
favor of the proper task args built into the framework. Just removing
the now unused arg now.

Author: nickvikeras

crates/sui-checkpoint-blob-indexer/src/main.rs

@@ -57,10 +57,6 @@ struct Args {
     #[arg(long)]
     compression_level: Option<i32>,
 
-    /// Optional watermark task name to override the watermark path
-    #[arg(long)]
-    watermark_task: Option<String>,
-
     #[command(flatten)]
     metrics_args: MetricsArgs,