Revert "Add Cronet trybots to all net changes."

This reverts commit 9a8baf49.

These bots don't have enough capacity to handle all net/ CLs, and
they've been blocking people from landing changes.

Bug: 712733
Change-Id: I270079658a22301553c998acff8ae2395d3e2fa3
Reviewed-on: https://chromium-review.googlesource.com/774958
Commit-Queue: Miriam Gershenson <mgersh@chromium.org>
Reviewed-by: Misha Efimov <mef@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517125}

net/PRESUBMIT.py

-# Copyright 2017 The Chromium Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-"""Presubmit script for net/.
-
-See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
-for more details about the presubmit API built into depot_tools.
-"""
-
-def PostUploadHook(cl, change, output_api):
-  """git cl upload will call this hook after the issue is created/modified.
-
-  This hook adds an extra line to the CL description in order to run Cronet
-  tests in addition to CQ bots.
-  """
-
-  # TODO(crbug.com/712733): Remove this once Cronet bots are deployed on CQ.
-  try_bots = ['master.tryserver.chromium.android:android_cronet_tester',
-              'master.tryserver.chromium.mac:ios-simulator-cronet']
-
-  return output_api.EnsureCQIncludeTrybotsAreAdded(
-    cl, try_bots, 'Automatically added Cronet trybots to run tests on CQ.')