sql-statements: improve SHOW TABLE REGIONS examples (pingcap#3389) (p…

…ingcap#3396)

* cherry pick pingcap#3389 to release-2.1

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>

* Delete sql-statement-show-table-regions.md

* Delete sql-statement-split-region.md

* Update TOC.md

Co-authored-by: Null not nil <67764674+nullnotnil@users.noreply.github.com>

TOC.md

@@ -216,11 +216,9 @@
       - [`SHOW [FULL] PROCESSSLIST`](/sql-statements/sql-statement-show-processlist.md)
       - [`SHOW SCHEMAS`](/sql-statements/sql-statement-show-schemas.md)
       - [`SHOW [FULL] TABLES`](/sql-statements/sql-statement-show-tables.md)
-      - [`SHOW TABLE REGIONS`](/sql-statements/sql-statement-show-table-regions.md)
       - [`SHOW TABLE STATUS`](/sql-statements/sql-statement-show-table-status.md)
       - [`SHOW [GLOBAL|SESSION] VARIABLES`](/sql-statements/sql-statement-show-variables.md)
       - [`SHOW WARNINGS`](/sql-statements/sql-statement-show-warnings.md)
-      - [`SPLIT REGION`](/sql-statements/sql-statement-split-region.md)
       - [`START TRANSACTION`](/sql-statements/sql-statement-start-transaction.md)
       - [`TRACE`](/sql-statements/sql-statement-trace.md)
       - [`TRUNCATE`](/sql-statements/sql-statement-truncate.md)