our example repositories snuck into the build dictionary.

Our internal_backend/repositories defines a couple of example repositories that our BUILD files can refer to.

Our BUILD Dictionary builder code looks at symbols defined in our BUILD files to figure out what do doc in http://pantsbuild.github.io/build_dictionary.html

So...

Give our old @manual.builddict() decorator a new optional arg, suppress.

Mark those example repositories with manual.builddict(suppress=True)

BUILD Dictionary builder checks for suppress==True and omits those

Testing Done:
publish_docs.sh , eyeballed

https://travis-ci.org/pantsbuild/pants/builds/36815549

Reviewed at https://rbcommons.com/s/twitter/r/1101/
Sync of https://github.com/pantsbuild/pants/commit/ad7d09d8964999d132c675bee5be634b16da808d