ddl: remove useless placement methods (#20636)
ddl: remove useless placement methods (#20636)

Signed-off-by: xhe <3cc054ec827480b50ed66e70bec75f34d9e09619@gmail.com>
XuHuaiyu/tidb,c4pt0r/tidb,c4pt0r/tidb,coocood/tidb,kyle-wang/tidb,ngaut/tidb,ngaut/tidb,XuHuaiyu/tidb,coocood/tidb,ngaut/tidb,c4pt0r/tidb,c4pt0r/tidb,kyle-wang/tidb,pingcap/tidb,c4pt0r/tidb,kyle-wang/tidb,pingcap/tidb,kyle-wang/tidb,ngaut/tidb,EvilMcJerkface/tidb,pingcap/tidb,pingcap/tidb,c4pt0r/tidb,pingcap/tidb,pingcap/tidb,kyle-wang/tidb,EvilMcJerkface/tidb,ngaut/tidb,ngaut/tidb,kyle-wang/tidb