Revert of Make gclient ready for the Blink (DEPS to main project) transition (patchset #6 id:180001 of https://codereview.chromium.org/743083002/)

Reason for revert:
The test intoruced is flake (see crrev.com/753543006/).
Need to look into that with more patience as it reproduces only on precise.


Original issue's description:
> Make gclient ready for the Blink (DEPS to main project) transition
> 
> This CL makes gclient understand correctly whether a git project is
> being moved from DEPS to an upper project and vice-versa.
> The driving use case for this is the upcoming Blink merge, where
> third_party/Webkit will be removed from DEPS (and .gitignore) and will 
> become part of the main project.
> 
> At present state, gclient leaves the .git folder around when a project
> is removed from DEPS, and that causes many problems. 
> 
> Furthermore this CL solves the performance problem of bisecting across
> the merge point. The subproject's (Blink) .git/ folder is moved to a
> backup location (in the main checkout root) and is restored when moving
> backwards, avoiding a re-fetch when bisecting across the merge point. 
> 
> BUG=431469
> 
> Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=293329

TBR=iannucci@chromium.org,maruel@chromium.org,jochen@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=431469

Review URL: https://codereview.chromium.org/796053002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@293352 0039d316-1c4b-4281-b951-d872f2087c98