remove the FK experiment mark

Signed-off-by: Yang Keao <[email protected]>

foreign-key.md

@@ -9,7 +9,6 @@ Starting from v6.6.0, TiDB supports the foreign key feature, which allows cross-
 
 > **Warning:**
 >
-> - Currently, the foreign key feature is experimental. It is not recommended that you use it in production environments. This feature might be changed or removed without prior notice. If you find a bug, you can report an [issue](https://github.com/pingcap/tidb/issues) on GitHub.
 > - The foreign key feature is typically employed to enforce [referential integrity](https://en.wikipedia.org/wiki/Referential_integrity) constraint checks. It might cause performance degradation, so it is recommended to conduct thorough testing before using it in performance-sensitive scenarios.
 
 The foreign key is defined in the child table. The syntax is as follows: