remove some duplicate FlipSign()
remove some duplicate FlipSign()

ApplyFilter2NoFlip is the new variant of ApplyFilter2 without the sign-flip

Change-Id: I2af54bd1499118c8321183e42251d265ba76219c

ttyangf/libwebp,rxl194/libwebp,redengineer/libwebp,zofuthan/libwebp,webmproject/libwebp,imazen/libwebp,webmproject/libwebp,yohunl/libwebp,ttyangf/libwebp,zofuthan/libwebp,Aexyn/libwebp,PKRoma/libwebp,yohunl/libwebp,imazen/libwebp,redengineer/libwebp,imazen/libwebp,zofuthan/libwebp,ya7lelkom/libwebp,Aexyn/libwebp,zofuthan/libwebp,PKRoma/libwebp,yohunl/libwebp,yohunl/libwebp,ttyangf/libwebp,rxl194/libwebp,rxl194/libwebp,Aexyn/libwebp,ya7lelkom/libwebp,ttyangf/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,redengineer/libwebp,ya7lelkom/libwebp,imazen/libwebp,webmproject/libwebp,PKRoma/libwebp,redengineer/libwebp,zofuthan/libwebp,imazen/libwebp,webmproject/libwebp,rxl194/libwebp,rxl194/libwebp,yohunl/libwebp,ya7lelkom/libwebp,ttyangf/libwebp,redengineer/libwebp,Aexyn/libwebp,ya7lelkom/libwebp,Aexyn/libwebp,PKRoma/libwebp