expression: remove useless functin fieldTypeFromPB (#9629)
expression: remove useless functin fieldTypeFromPB (#9629)


kyle-wang/tidb,coocood/tidb,kyle-wang/tidb,ngaut/tidb,ngaut/tidb,ngaut/tidb,kyle-wang/tidb,c4pt0r/tidb,Cofyc/tidb,pingcap/tidb,ngaut/tidb,cosmtrek/tidb,c4pt0r/tidb,ming-relax/tidb,c4pt0r/tidb,ngaut/tidb,pingcap/tidb,cosmtrek/tidb,qiuyesuifeng/tidb,c4pt0r/tidb,pingcap/tidb,kyle-wang/tidb,EvilMcJerkface/tidb,kyle-wang/tidb,ming-relax/tidb,pingcap/tidb,qiuyesuifeng/tidb,pingcap/tidb,XuHuaiyu/tidb,c4pt0r/tidb,c4pt0r/tidb,ngaut/tidb,pingcap/tidb,XuHuaiyu/tidb,kyle-wang/tidb,Cofyc/tidb,EvilMcJerkface/tidb,coocood/tidb