Remove some unused proxy-related histograms.

Remove some unused proxy-related histograms.

These histograms are no longer being monitored, so removing them from Chromium.

 - Net.DhcpWpad*
 - Net.MTPR_*
 - Net.ProxyResolver*
 - Net.ProxyPollConfigurationTime [1]
 - Net.GetProxyForURL*:  [1]

[1] Removed from histograms.xml; the histogram is not present in the code.

Committed: https://crrev.com/7f1ac491eb1c33fb7a22dce12fe01551ae2d8475
Cr-Commit-Position: refs/heads/master@{#295105}

[eroman, 2014-09-15 23:34:50]

Patchset #1 (id:1) has been deleted

[eroman, 2014-09-15 23:35:28]

eroman@chromium.org changed reviewers:
+ ellyjones@chromium.org, isherman@chromium.org

[eroman, 2014-09-15 23:35:29]

@ellyjones: for the net code changes

@isherman: for histograms.xml (Is it recommended to delete old histograms or
mark them as obsolete?)

[Ilya Sherman, 2014-09-15 23:39:59]

Please mark all of the removed histograms as <obsolete> rather than deleting
them.

[eroman, 2014-09-15 23:54:36]

Done. There are 3 for which I do not know the history, so I marked them as:

  <obsolete>
    Removed at some time before 2014/09/15.
  </obsolete>

[Ilya Sherman, 2014-09-16 00:00:54]

Thanks.  Histograms LGTM.

[Elly Fong-Jones, 2014-09-16 14:56:57]

On 2014/09/16 00:00:54, Ilya Sherman wrote:
> Thanks.  Histograms LGTM.

network code lgtm

[eroman, 2014-09-16 17:27:03]

The CQ bit was checked by eroman@chromium.org

[commit-bot: I haz the power, 2014-09-16 17:28:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/573893004/40001

[commit-bot: I haz the power, 2014-09-16 18:26:43]

Committed patchset #2 (id:40001) as 0b3bd4f871d17cc4323859411dcc0c0bc28da862

[commit-bot: I haz the power, 2014-09-16 18:28:54]

Patchset 2 (id:??) landed as
https://crrev.com/7f1ac491eb1c33fb7a22dce12fe01551ae2d8475
Cr-Commit-Position: refs/heads/master@{#295105}