tiflash: Remove the description about expr_blacklist in use_tiflash.md (

#6188) (#6279)

tiflash/use-tiflash.md

@@ -245,14 +245,12 @@ Currently, TiFlash supports the following push-down expressions:
 * Logical functions: `and, or, not, case when, if, ifnull, isnull, in, like, coalesce`
 * Bitwise operations: `bitand, bitor, bigneg, bitxor`
 * String functions: `substr, char_length, replace, concat, concat_ws, left, right, ascii, length, trim, position`
-* Date functions: `date_format, timestampdiff, from_unixtime, unix_timestamp(int), unix_timestamp(decimal), str_to_date(date), str_to_date(datetime), date_add(datetime, int), date_add(string, int), date_add(string, real), date_sub(datetime, int), date_sub(string, int), datediff, year, month, day, extract(datetime), date`
+* Date functions: `date_format, timestampdiff, from_unixtime, unix_timestamp(int), unix_timestamp(decimal), str_to_date(date), str_to_date(datetime), datediff, year, month, day, extract(datetime), date`
 * JSON function: `json_length`
 * Conversion functions: `cast(int as double), cast(int as decimal), cast(int as string), cast(int as time), cast(double as int), cast(double as decimal), cast(double as string), cast(double as time), cast(string as int), cast(string as double), cast(string as decimal), cast(string as time), cast(decimal as int), cast(decimal as string), cast(decimal as time), cast(time as int), cast(time as decimal), cast(time as string)`
 * Aggregate functions: `min, max, sum, count, avg, approx_count_distinct`
 * Miscellaneous functions: `inetntoa, inetaton, inet6ntoa, inet6aton`
 
-Among them, the push-down of `cast` and `date_add` is not enabled by default. To enable it, refer to [Blocklist of Optimization Rules and Expression Pushdown](/blocklist-control-plan.md).
-
 In addition, expressions that contain the Time/Bit/Set/Enum/Geometry type cannot be pushed down to TiFlash.
 
 If a query encounters unsupported push-down calculations, TiDB needs to complete the remaining calculations, which might greatly affect the TiFlash acceleration effect. The currently unsupported operators and expressions might be supported in future versions.