Remove "url" from Elasticsearch index

Summary:
Ref T12450. This was added a very very long time ago (D2298).

I don't want to put this in the upstream index anymore because I don't want to encourage third parties to develop software which reads the index directly. Reading the index directly is a big skeleton key which bypasses policy checks.

This was added before much of the policy model existed, when that wasn't as much of a concern. On a tecnhnical note, this also doesn't update when phabricator.base-uri changes.

This can be written as a search index extension if an install relies on it for some bizarre reason, although none should and I'm unaware of any actual use cases in the wild for it, even at Facebook.

Test Plan: Indexed some random stuff into ElasticSearch.

Reviewers: chad, 20after4

Reviewed By: chad

Maniphest Tasks: T12450

Differential Revision: https://secure.phabricator.com/D17600