This reverts commit 0c91147d.

Reason for revert: This is causing 'gclient revinfo' to fail on the release builders, and appears to be somehow related to the "--output-json" flag.

Original change's description:
> gclient: Don't allow None URLs (except in .gclient files)
> 
> This reverts commit crrev.com/4e9b50ab
> and thus relands the following commits:
> 
>   ebdd0db4: "gclient: Remove URLs from hierarchy."
>   54a5c2ba: "gclient: Refactor PrintRevInfo"
>   083eb25f: "gclient: Don't allow URL to be None."
> 
> When a None URL is specified in a .gclient file, and a DEPS file is
> given, the DEPS file is treated as a .gclient file and its dependencies
> are added.
> 
> Bug: 839925
> 
> Change-Id: I1068b66487874bfa0a788bf9da5273714b6ad39e
> Reviewed-on: https://chromium-review.googlesource.com/1083340
> Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
> Reviewed-by: Aaron Gable <agable@chromium.org>
> Reviewed-by: Michael Moss <mmoss@chromium.org>

TBR=agable@chromium.org,mmoss@chromium.org,ehmaldonado@chromium.org

Change-Id: I46785bd272b16b3672e553b6443cee6d6b370ec1
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 839925, 853093
Reviewed-on: https://chromium-review.googlesource.com/1101978Reviewed-by: Michael Moss <mmoss@chromium.org>
Commit-Queue: Michael Moss <mmoss@chromium.org>