Revert of git cl: Rework Changelist class for Rietveld/Gerrit use. (patchset #8 id:380001 of https://codereview.chromium.org/1805193002/ )

Reason for revert:
Broke one project presubmit.

Original issue's description:
> git cl: Rework Changelist class for Rietveld/Gerrit use.
> 
> This adds pluggable codereview-specific implementations into
> Changelist class. The specific implementation is chosen at
> Changelist automatically, with Rietveld being default for
> backwards compatibility.
> 
> Gerrit implementation for Gerrit is incomplete, and will be
> added in later CLs. However, it is sufficient to ensure
> current functionality of this tool is not diminished.
> 
> Sadly, the base class isn't completely free from Rietveld
> assumptions because of presubmit_support. Apparently, PRESUBMIT 
> scripts can make use of Rietveld instance for RPCs directly.
> This use doesn't make sense for Gerrit, which substitutes
> rietveld instance with a dummy object, which raises exception
> on any attribute access with a diagnostic message.
> 
> This also includes refactoring of some related code which
> (ab)used ChangeList. Overall, this CL adds a few extra call to
> git config in order to determine which codereview to use, but
> but it shouldn't have any performance impact.
> 
> 
> BUG=579160
> 
> Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=299462

TBR=phajdan.jr@chromium.org,andybons@chromium.org,machenbach@chromium.org,sergiyb@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=579160,597638

Review URL: https://codereview.chromium.org/1831813003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299476 0039d316-1c4b-4281-b951-d872f2087c98