Bump iossim default device to 'iPhone 5s'.

Bump iossim default device to 'iPhone 5s'.

iOS builds now default to 64-bit (codereview.chromium.org/1021513002). Bump
default device to iPhone 5s, which supports 64-bit binaries.

BUG=None
TEST=iossim works without passing any device flags.

Committed: https://crrev.com/cb1a6ec0053492be868f52711138cf3f158e71f9
Cr-Commit-Position: refs/heads/master@{#324283}

[justincohen, 2015-04-08 18:39:30]

justincohen@chromium.org changed reviewers:
+ rohitrao@chromium.org

[justincohen, 2015-04-08 18:39:31]

PTAL

[rohitrao (ping after 24h), 2015-04-08 18:52:00]

lgtm

[justincohen, 2015-04-08 18:53:34]

The CQ bit was checked by justincohen@chromium.org

[commit-bot: I haz the power, 2015-04-08 18:54:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1070753004/1

[commit-bot: I haz the power, 2015-04-08 20:55:03]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-08 20:56:27]

Patchset 1 (id:??) landed as
https://crrev.com/cb1a6ec0053492be868f52711138cf3f158e71f9
Cr-Commit-Position: refs/heads/master@{#324283}