Delete deprecated tiflash configs (#11646) (#11692)

tiflash/tiflash-configuration.md

@@ -68,12 +68,8 @@ delta_index_cache_size = 0
 
 ## Storage paths settings take effect starting from v4.0.9
 [storage]
-    ## This configuration item is deprecated since v5.2.0. You can use the [storage.io_rate_limit] settings below instead.
-
-    # bg_task_io_rate_limit = 0
 
     ## DTFile format
-    ## * format_version = 1, the old format, deprecated.
     ## * format_version = 2, the default format for versions < v6.0.0.
     ## * format_version = 3, the default format for v6.0.0 and v6.1.x, which provides more data validation features.
     ## * format_version = 4, the default format for v6.2.0 and later versions, which reduces write amplification and background task resource consumption