expression: remove useless code (#4186)
expression: remove useless code (#4186)


tiancaiamao/tidb,Cofyc/tidb,coocood/tidb,pingcap/tidb,EvilMcJerkface/tidb,louishust/tidb,coocood/tidb,XuHuaiyu/tidb,ngaut/tidb,tiancaiamao/tidb,8cbx/tidb,ming-relax/tidb,pingcap/tidb,yangwenmai/tidb,zimulala/tidb,XuHuaiyu/tidb,kyle-wang/tidb,kyle-wang/tidb,cosmtrek/tidb,pingcap/tidb,ngaut/tidb,ngaut/tidb,yuanwhy/tidb,c4pt0r/tidb,EvilMcJerkface/tidb,yangwenmai/tidb,cosmtrek/tidb,kyle-wang/tidb,c4pt0r/tidb,qiuyesuifeng/tidb,kyle-wang/tidb,ngaut/tidb,Nify/tidb,c4pt0r/tidb,c4pt0r/tidb,gaocegege/tidb,ngaut/tidb,louishust/tidb,yuanwhy/tidb,qiuyesuifeng/tidb,gaocegege/tidb,c4pt0r/tidb,mccxj/tidb,8cbx/tidb,mccxj/tidb,ming-relax/tidb,ngaut/tidb,c4pt0r/tidb,spongedu/tidb,pingcap/tidb,zimulala/tidb,Nify/tidb,spongedu/tidb,kyle-wang/tidb,wusphinx/tidb,wusphinx/tidb,pingcap/tidb,CodeRushing/tidb,pingcap/tidb,CodeRushing/tidb,kyle-wang/tidb,Cofyc/tidb