VS 2015 supplies a conforming snprintf implementation, so #define
snprintf is no longer needed. Also, VS 2015 checks for #define of
snprintf and treats it as a fatal error.

LOG=Y
R=jarin@chromium.org
BUG=440500

Review URL: https://codereview.chromium.org/1078453002

Cr-Commit-Position: refs/heads/master@{#27690}