Remove unused blocking pool methods from web::WebThread.

ios/web/public/web_thread.h

Index: ios/web/public/web_thread.h
diff --git a/ios/web/public/web_thread.h b/ios/web/public/web_thread.h
index be41b3080b58b14866953e8ab4464abf0c93c1da..0ab786caa664456a5f132e6249cadadd10488b5a 100644
--- a/ios/web/public/web_thread.h
+++ b/ios/web/public/web_thread.h
@@ -139,38 +139,6 @@ class WebThread {
     return GetTaskRunnerForThread(identifier)->DeleteSoon(from_here, object);
   }
 
-  // Simplified wrappers for posting to the blocking thread pool. Use this
-  // for doing things like blocking I/O.
-  //
-  // The first variant will run the task in the pool with no sequencing
-  // semantics, so may get run in parallel with other posted tasks. The second
-  // variant will all post a task with no sequencing semantics, and will post a
-  // reply task to the origin TaskRunner upon completion.  The third variant
-  // provides sequencing between tasks with the same sequence token name.
-  //
-  // These tasks are guaranteed to run before shutdown.
-  //
-  // If you need to provide different shutdown semantics (like you have
-  // something slow and noncritical that doesn't need to block shutdown),
-  // or you want to manually provide a sequence token (which saves a map
-  // lookup and is guaranteed unique without you having to come up with a
-  // unique string), you can access the sequenced worker pool directly via
-  // GetBlockingPool().
-  //
-  // If you need to PostTaskAndReplyWithResult, use
-  // base::PostTaskAndReplyWithResult() with GetBlockingPool() as the task
-  // runner.
-  static bool PostBlockingPoolTask(const tracked_objects::Location& from_here,
-                                   base::OnceClosure task);
-  static bool PostBlockingPoolTaskAndReply(
-      const tracked_objects::Location& from_here,
-      base::OnceClosure task,
-      base::OnceClosure reply);
-  static bool PostBlockingPoolSequencedTask(
-      const std::string& sequence_token_name,
-      const tracked_objects::Location& from_here,
-      base::OnceClosure task);
-
   // Returns the thread pool used for blocking file I/O. Use this object to
   // perform random blocking operations such as file writes.
   static base::SequencedWorkerPool* GetBlockingPool() WARN_UNUSED_RESULT;