Remove allow-auto-random from config manual (pingcap#4037)

Co-authored-by: TomShawn <[email protected]>

Author: Joyinqin

troubleshoot-hot-spot-issues.md

@@ -120,15 +120,6 @@ As shown in the load diagrams above, before setting `SHARD_ROW_ID_BITS`, load ho
 
 To resolve the write hotspots brought by auto-increment primary keys, use `AUTO_RANDOM` to handle hotspot tables that have auto-increment primary keys.
 
-> **Note:**
->
-> Currently, this is an experimental feature, so it is not recommended to use it in the production environment. To enable this feature, use the following configuration:
->
-> ```
-> [experimental]
-> allow-auto-random = true
-> ```
-
 If this feature is enabled, TiDB generates randomly distributed and non-repeated (before the space is used up) primary keys to achieve the purpose of scattering write hotspots.
 
 Note that the primary keys generated by TiDB are no longer auto-increment primary keys and you can use `LAST_INSERT_ID()` to obtain the primary key value assigned last time.