win: Remove unused function after https://codereview.chromium.org/2143893002

Fixes a Wunused-function build error in official win builds with clang.

BUG=600915,82385
TBR=calamity@chromium.org

Review URL: https://codereview.chromium.org/2203623003 .

Cr-Commit-Position: refs/heads/master@{#409171}
1 file changed