Remove unused methods from URLRequest.

Remove unused methods from URLRequest.

Remove methods to get/set headers by "ID", which were never
implemented and have existed since initial commit.

Also remove GetAllResponseHeaders, which returns all response
headers in a single string with NULL characters between headers.
Shockingly, nothing is using this method.

BUG=455744
Committed: https://crrev.com/90948ab7b3ced4cd727f92980de46eff6fdd69b2
Cr-Commit-Position: refs/heads/master@{#314852}

[mmenke, 2015-02-05 17:11:19]

mmenke@chromium.org changed reviewers:
+ davidben@chromium.org

[mmenke, 2015-02-05 17:11:20]

Mind reviewing this (And a couple CLs like it)?  Think you're the only network
stack team member other than I who's touched this class in the last year...And
these should be fast reviews, anyways.

[davidben, 2015-02-05 18:22:12]

lgtm!

> Think you're the only network stack team member other than I who's touched
this class in the last year...

Really? Merp.

[davidben, 2015-02-05 18:22:13]

lgtm!

> Think you're the only network stack team member other than I who's touched
this class in the last year...

Really? Merp.

[mmenke, 2015-02-05 18:24:37]

On 2015/02/05 18:22:13, David Benjamin wrote:
> lgtm!
> 
> > Think you're the only network stack team member other than I who's touched
> this class in the last year...
> 
> Really? Merp.

Thanks!

At least it means any recently added bloat to the interface is other team's
fault (Well...or mine)...  Which I guess is a good thing?

[mmenke, 2015-02-05 18:25:07]

The CQ bit was checked by mmenke@chromium.org

[commit-bot: I haz the power, 2015-02-05 18:25:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/905503003/20001

[commit-bot: I haz the power, 2015-02-05 19:21:25]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-05 19:22:36]

Patchset 2 (id:??) landed as
https://crrev.com/90948ab7b3ced4cd727f92980de46eff6fdd69b2
Cr-Commit-Position: refs/heads/master@{#314852}