Revert of ipc: Add a new field num_brokered_attachments to the message header.

Revert of ipc: Add a new field num_brokered_attachments to the message header. (patchset #1 id:1 of https://codereview.chromium.org/1311673011/ )

Reason for revert:
Causes crashes on Canary:
https://code.google.com/p/chromium/issues/detail?id=524032

Original issue's description:
> ipc: Add a new field num_brokered_attachments to the message header.
>
> BUG=493414
>
> Committed: https://crrev.com/9e3e945e56139cf34634dc21ad25a67fc5507590
> Cr-Commit-Position: refs/heads/master@{#346426}

TBR=tsepez@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=493414
Committed: https://crrev.com/01eb81a73adc66c3e8a5385ec6aed81a93450940
Cr-Commit-Position: refs/heads/master@{#346692}

[erikchen, 2015-09-01 18:24:35]

Created Revert of ipc: Add a new field num_brokered_attachments to the message
header.

[commit-bot: I haz the power, 2015-09-01 18:24:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1326703002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1326703002/1

[commit-bot: I haz the power, 2015-09-01 18:25:54]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-01 18:26:47]

Patchset 1 (id:??) landed as
https://crrev.com/01eb81a73adc66c3e8a5385ec6aed81a93450940
Cr-Commit-Position: refs/heads/master@{#346692}