util/types: clean up for golint
util/types: clean up for golint

Cofyc/tidb,JinheLin/tidb,EvilMcJerkface/tidb,anywhy/tidb,cosmtrek/tidb,yangwenmai/tidb,myrice/tidb,c4pt0r/tidb,silenceper/tidb,gaocegege/tidb,silentred/tidb,yangwenmai/tidb,zimulala/tidb,CodeRushing/tidb,Nify/tidb,cosmtrek/tidb,kyle-wang/tidb,ngaut/tidb,netroby/tidb,simon-xia/tidb,kyle-wang/tidb,astaxie/tidb,qhsong/tidb,qhsong/tidb,8cbx/tidb,liyu4/tidb,EvilMcJerkface/tidb,ngaut/tidb,coocood/tidb,8cbx/tidb,ming-relax/tidb,andelf/tidb,anywhy/tidb,gaocegege/tidb,pingcap/tidb,ngaut/tidb,zimulala/tidb,tiancaiamao/tidb,CodeRushing/tidb,wusphinx/tidb,pingcap/tidb,yuanwhy/tidb,kyle-wang/tidb,spongedu/tidb,louishust/tidb,spongedu/tidb,ueizhou/tidb,yuanwhy/tidb,silenceper/tidb,astaxie/tidb,XuHuaiyu/tidb,coocood/tidb,zs634134578/tidb,andelf/tidb,c4pt0r/tidb,pingcap/tidb,Nify/tidb,liyu4/tidb,ngaut/tidb,pingcap/tidb,XuHuaiyu/tidb,tiancaiamao/tidb,ueizhou/tidb,louishust/tidb,c4pt0r/tidb,wusphinx/tidb,simon-xia/tidb,qiuyesuifeng/tidb,ngaut/tidb,Cofyc/tidb,kyle-wang/tidb,silentred/tidb,c4pt0r/tidb,JinheLin/tidb,mccxj/tidb,c4pt0r/tidb,kyle-wang/tidb,zs634134578/tidb,ngaut/tidb,mccxj/tidb,kyle-wang/tidb,myrice/tidb,c4pt0r/tidb,pingcap/tidb,netroby/tidb,pingcap/tidb,qiuyesuifeng/tidb,ming-relax/tidb