__STDC_FORMAT_MACROS are already set for all chromium code, no need to set it again just for blink in config.h.

Review URL: https://codereview.chromium.org/165443002

git-svn-id: svn://svn.chromium.org/blink/trunk@167158 bbb929c8-8fbe-4397-9dbb-9b2b20218538