Remove unnecessary dependency on system_wrappers in libjingle.

Remove unnecessary dependency on system_wrappers in libjingle.

The system_wrappers target is already included due to the dependency
on the <(DEPTH)/third_party/webrtc/webrtc.gyp:webrtc target.

Committed: https://crrev.com/056fa7bf2713b8611bf5cb0069cac5a7989d9b09
Cr-Commit-Position: refs/heads/master@{#311455}

[kjellander_chromium, 2015-01-14 10:34:36]

kjellander@chromium.org changed reviewers:
+ perkj@chromium.org

[kjellander_chromium, 2015-01-14 10:34:37]

This is causing trouble due to restructuring in
https://code.google.com/p/webrtc/source/detail?r=8057

[perkj_chrome, 2015-01-14 10:35:47]

lgtm

[kjellander_chromium, 2015-01-14 11:29:41]

The CQ bit was checked by kjellander@chromium.org

[commit-bot: I haz the power, 2015-01-14 11:30:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/851873004/1

[commit-bot: I haz the power, 2015-01-14 11:39:01]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-14 11:40:56]

Patchset 1 (id:??) landed as
https://crrev.com/056fa7bf2713b8611bf5cb0069cac5a7989d9b09
Cr-Commit-Position: refs/heads/master@{#311455}