removed redundant is_dirty function
removed redundant is_dirty function

elelianghh/sqlalchemy,j5int/sqlalchemy,ThiefMaster/sqlalchemy,276361270/sqlalchemy,robin900/sqlalchemy,itkovian/sqlalchemy,Akrog/sqlalchemy,pdufour/sqlalchemy,halfcrazy/sqlalchemy,hsum/sqlalchemy,sandan/sqlalchemy,sandan/sqlalchemy,graingert/sqlalchemy,bdupharm/sqlalchemy,j5int/sqlalchemy,sqlalchemy/sqlalchemy,inspirehep/sqlalchemy,EvaSDK/sqlalchemy,wfxiang08/sqlalchemy,bootandy/sqlalchemy,276361270/sqlalchemy,zzzeek/sqlalchemy,alex/sqlalchemy,Akrog/sqlalchemy,graingert/sqlalchemy,bootandy/sqlalchemy,wfxiang08/sqlalchemy,itkovian/sqlalchemy,inspirehep/sqlalchemy,brianv0/sqlalchemy,olemis/sqlalchemy,davidjb/sqlalchemy,davidjb/sqlalchemy,olemis/sqlalchemy,epa/sqlalchemy,WinterNis/sqlalchemy,epa/sqlalchemy,monetate/sqlalchemy,wujuguang/sqlalchemy,dstufft/sqlalchemy,monetate/sqlalchemy,davidfraser/sqlalchemy,davidfraser/sqlalchemy,bdupharm/sqlalchemy,brianv0/sqlalchemy,EvaSDK/sqlalchemy,Cito/sqlalchemy,wujuguang/sqlalchemy,hsum/sqlalchemy,pdufour/sqlalchemy,robin900/sqlalchemy,elelianghh/sqlalchemy,alex/sqlalchemy,Cito/sqlalchemy,dstufft/sqlalchemy,Cito/sqlalchemy,halfcrazy/sqlalchemy,ThiefMaster/sqlalchemy,alex/sqlalchemy,WinterNis/sqlalchemy