ios: Remove redundant c++11 setting.
ios: Remove redundant c++11 setting.

The line
              'CLANG_CXX_LANGUAGE_STANDARD': 'c++11',  # -std=c++11
in the shared "mac or ios" section further up already has this effect.
No behavior change.

BUG=none

Review URL: https://codereview.chromium.org/1410153002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#354638}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk