Revert of Reland #2 "ipc: Add a new field num_brokered_attachments to the message header."

Revert of Reland #2 "ipc: Add a new field num_brokered_attachments to the message header." (patchset #5 id:80001 of https://codereview.chromium.org/1334593002/ )

Reason for revert:
CL was only ever intended to be in 1 canary release.

Original issue's description:
> Reland #2 "ipc: Add a new field num_brokered_attachments to the message header."
>
> This original version of this CL is causing an unusual crash in Canary. This CL
> adds a message verifier to the ipc code so that it can dynamically verify the
> contents of this message that is being corrupted. This CL also verifies the
> message at several different points in the dispatch process. This will help
> narrow down the range of code that is corrupting the message.
>
> I expect this CL to cause ~100 crashes in the next Chrome Canary. I intend to
> revert this CL after a single Canary release.
>
> BUG=527588
>
> Committed: https://crrev.com/a2e71be46dc4bdcbb544db479680f65a390ae8f3
> Cr-Commit-Position: refs/heads/master@{#349056}

TBR=avi@chromium.org,tsepez@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=527588
Committed: https://crrev.com/1fa7dad91bc711eb1e481aa467a2f38c77cdae54
Cr-Commit-Position: refs/heads/master@{#349152}

[erikchen, 2015-09-16 17:33:45]

Created Revert of Reland #2 "ipc: Add a new field num_brokered_attachments to
the message header."

[commit-bot: I haz the power, 2015-09-16 17:34:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1350823002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1350823002/1

[commit-bot: I haz the power, 2015-09-16 17:35:14]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-16 17:36:24]

Patchset 1 (id:??) landed as
https://crrev.com/1fa7dad91bc711eb1e481aa467a2f38c77cdae54
Cr-Commit-Position: refs/heads/master@{#349152}

[commit-bot: I haz the power, 2015-09-23 12:57:20]

Patchset 1 (id:??) landed as
https://crrev.com/1fa7dad91bc711eb1e481aa467a2f38c77cdae54
Cr-Commit-Position: refs/heads/master@{#349152}