MDEV-25211 Remove useless counter Innodb_buffered_aio_submitted

In commit 412533b4a755b36d5ac0fb04bcf54694bb0eafbc (MDEV-18582),
one of the counters that was ported from XtraDB is useless.
Innodb_buffered_aio_submitted would be 0 or 1, depending on whether
is_linux_native_aio_supported() was executed to the point where
it would be incremented.

Let us remove this counter, because it has no practical value.
Even if its value were 1, io_setup() can still fail and we may
end up with innodb_use_native_aio=0.

storage/innobase/handler/ha_innodb.cc

@@ -866,9 +866,6 @@ static SHOW_VAR innodb_status_variables[]= {
   {"adaptive_hash_non_hash_searches", &btr_cur_n_non_sea, SHOW_SIZE_T},
 #endif
   {"background_log_sync", &srv_log_writes_and_flush, SHOW_SIZE_T},
-#if defined(LINUX_NATIVE_AIO)
-  {"buffered_aio_submitted", &srv_stats.buffered_aio_submitted, SHOW_SIZE_T},
-#endif
   {"buffer_pool_dump_status",
   (char*) &export_vars.innodb_buffer_pool_dump_status,	  SHOW_CHAR},
   {"buffer_pool_load_status",

storage/innobase/include/srv0srv.h

@@ -81,10 +81,6 @@ struct srv_stats_t
 	space in the log buffer and have to flush it */
 	ulint_ctr_1_t		log_waits;
 
-#if defined(LINUX_NATIVE_AIO)
-	ulint_ctr_1_t buffered_aio_submitted;
-#endif
-
 	/** Store the number of write requests issued */
 	ulint_ctr_1_t		buf_pool_write_requests;
 

storage/innobase/os/os0file.cc

@@ -3963,7 +3963,6 @@ static bool is_linux_native_aio_supported()
 	}
 
 	int	err = io_submit(io_ctx, 1, &p_iocb);
-	srv_stats.buffered_aio_submitted.inc();
 
 	if (err >= 1) {
 		/* Now collect the submitted IO request. */