[r=gz] testing/checkers: Cleanup SameContent checker
[r=gz] testing/checkers: Cleanup SameContent checker

Trivial followup on some missed review comments from initial implementation:

<https://codereview.appspot.com/13082044/>

Remove redundant comment, and simplify some of the code by using the property
that the expected and obtained slice lengths are checked for equivalence.

https://codereview.appspot.com/13411045/

R=jameinel
ericsnowcurrently/juju,marcmolla/juju,alesstimec/juju,alesstimec/juju,bac/juju,anastasiamac/juju,cloud-green/juju,mattyw/juju,jrwren/juju,macgreagoir/juju,marcmolla/juju,alesstimec/juju,bogdanteleaga/juju,waigani/juju,frankban/juju,reedobrien/juju,mhilton/juju-juju,sinzui/juju,Altoros/juju-vmware,cmars/juju,fwereade/juju,cherylj/juju,tsakas/juju,mjs/juju,gabriel-samfira/juju,macgreagoir/juju,rogpeppe/juju,frankban/juju-tmp,macgreagoir/juju,frankban/juju,tsakas/juju,dimitern/juju,rogpeppe/juju,thomnico/juju,cmars/juju,tasdomas/juju,AdamIsrael/juju,tasdomas/juju,frankban/juju,thomnico/juju,jrwren/juju,voidspace/juju,marcmolla/juju,dimitern/juju,cloud-green/juju,kat-co/juju,wwitzel3/juju,Altoros/juju-vmware,macgreagoir/juju,mjs/juju,mikemccracken/juju,bac/juju,Altoros/juju-cloudsigma,kat-co/juju,sinzui/juju,axw/juju,gabriel-samfira/juju,mhilton/juju,mhilton/juju-juju,tsakas/juju,dooferlad/juju,mhilton/juju,tych0/juju,tych0/juju,marcoceppi/juju,sinzui/juju,wwitzel3/juju,frankban/juju,reedobrien/juju,dimitern/juju,sinzui/juju,mattyw/juju,mhilton/juju-juju,anastasiamac/juju,frankban/juju-tmp,marcoceppi/juju,tasdomas/juju,makyo/juju,howbazaar/juju,bogdanteleaga/juju,bz2/juju,frankban/juju-tmp,cloud-green/juju,cmars/juju,davecheney/juju,AdamIsrael/juju,marcmolla/juju,alesstimec/juju,dooferlad/juju,mjs/juju,waigani/juju,makyo/juju,perrito666/juju,cherylj/juju,Altoros/juju-vmware,frankban/juju-tmp,waigani/juju,mhilton/juju,Altoros/juju-vmware,davecheney/juju,voidspace/juju,axw/juju,kat-co/juju,thomnico/juju,tsakas/juju,frobware/juju,frobware/juju,mjs/juju,reedobrien/store,AdamIsrael/juju,dooferlad/juju,macgreagoir/juju,Altoros/juju-cloudsigma,dooferlad/juju,cloud-green/juju,makyo/juju,bac/juju,anastasiamac/juju,perrito666/juju,tych0/juju,kat-co/juju,bogdanteleaga/juju,marcoceppi/juju,voidspace/juju,bz2/juju,mhilton/juju-juju,mattyw/juju,bz2/juju,Altoros/juju-cloudsigma,ericsnowcurrently/juju,axw/juju,ericsnowcurrently/juju,Altoros/juju-cloudsigma,frankban/juju,axw/juju,perrito666/juju,fwereade/juju,reedobrien/juju,ericsnowcurrently/juju,bac/juju,kat-co/juju,mjs/juju,perrito666/juju,voidspace/juju,howbazaar/juju,dimitern/juju,mikemccracken/juju,bogdanteleaga/juju,thomnico/juju,gabriel-samfira/juju,davecheney/juju,gabriel-samfira/juju,anastasiamac/juju,ericsnowcurrently/juju,marcmolla/juju,mattyw/juju,cherylj/juju,howbazaar/juju,tasdomas/juju,jrwren/juju,gabriel-samfira/juju,bac/juju,wwitzel3/juju,reedobrien/juju,axw/juju,bz2/juju,mjs/juju,alesstimec/juju,fwereade/juju,anastasiamac/juju,rogpeppe/juju,dooferlad/juju,mjs/juju,perrito666/juju,mikemccracken/juju,wwitzel3/juju,howbazaar/juju,makyo/juju,reedobrien/juju,cmars/juju,davecheney/juju,frobware/juju,howbazaar/juju,AdamIsrael/juju,tych0/juju,mikemccracken/juju,mhilton/juju,mikemccracken/juju,waigani/juju,marcoceppi/juju,bz2/juju,dimitern/juju,cherylj/juju,fwereade/juju