Remove superfulous _.identitys
Remove superfulous _.identitys

By removing these we avoid unnecessarily transforming out predicate through
`optimizeCb()`.

tnga/underscore-es,rlugojr/underscore,jpalomar/underscore,documentcloud/underscore,jpalomar/underscore,keepgoingwm/underscore,jdelbello/underscore,akre54/underscore,documentcloud/underscore,tnga/underscore-es,jashkenas/underscore,jdelbello/underscore,akre54/underscore,rlugojr/underscore,jashkenas/underscore,keepgoingwm/underscore