Removes Solr configuration from aws-config.

Summary:
Solr has not yet been uninstalled from production-rpc. I will do so
after this revision lands and ensuring there are no objections.

I will make a backup of all of our data in Solr before I bring it down.

production-rpc is still reverse proxying CloudSearch and I left the
logic for that in the configuration. I also kept the Vagrantfile and
related scripts because they are useful when testing changes to our
configuration scripts (it's also cheap to keep since they're already
there).

In some places we make reference to `solr_secret` despite Solr no
longer being around. This is because our `secrets.py` file still calls
the shared secret `solr_secret`. I don't have the ability to change
this as far as I can tell, and haven't gotten around to poking anybody
to do so. So it remains as `solr_secret` at this time.

Test Plan:
- Ran `vagrant up` and then ran a full search indexing job in the
  webapp to ensure the reverse proxy functioned correctly.

Reviewers: benkomalo, csilvers

Reviewed By: csilvers

Maniphest Tasks: T2389

Differential Revision: http://phabricator.khanacademy.org/D10162