Remove some unused NaCl srpc methods (AttachService, ctor variant)

Remove some unused NaCl srpc methods (AttachService, ctor variant).

Remove a couple unused fwd declarations and make a Getter
const while I'm messing with that file.

BUG=none

Committed: https://crrev.com/88fe77f9b9d4395f36b0b140ab4dcefc61bfecc3
Cr-Commit-Position: refs/heads/master@{#319159}

[jvoung (off chromium), 2015-03-04 20:33:19]

jvoung@chromium.org changed reviewers:
+ dschuff@chromium.org

[Derek Schuff, 2015-03-04 21:21:45]

lgtm

[jvoung (off chromium), 2015-03-04 22:24:17]

The CQ bit was checked by jvoung@chromium.org

[commit-bot: I haz the power, 2015-03-04 22:25:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/977893003/20001

[commit-bot: I haz the power, 2015-03-04 23:20:37]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-03-04 23:21:04]

Patchset 2 (id:??) landed as
https://crrev.com/88fe77f9b9d4395f36b0b140ab4dcefc61bfecc3
Cr-Commit-Position: refs/heads/master@{#319159}