gclient: remove support for From()

This feature appears unused, and removing it will simplify the codebase.

Bug: 661382
Change-Id: I545befb2c592eea53c54552018ce2d3dda7670f5
Reviewed-on: https://chromium-review.googlesource.com/509693
Commit-Queue: Paweł Hajdan Jr. <phajdan.jr@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
diff --git a/gclient_utils.py b/gclient_utils.py
index d46dbd1..8fe0c5e 100644
--- a/gclient_utils.py
+++ b/gclient_utils.py
@@ -813,8 +813,7 @@
   """Runs a set of WorkItem that have interdependencies and were WorkItem are
   added as they are processed.
 
-  In gclient's case, Dependencies sometime needs to be run out of order due to
-  From() keyword. This class manages that all the required dependencies are run
+  This class manages that all the required dependencies are run
   before running each one.
 
   Methods of this class are thread safe.