angle: move DeallocateCurrent into windows only code DeallocateCurrent is only called from within DllMain, which means it's only called on windows. On the mac, the warning unused-function may be triggered. Move DeallocateCurrent to windows only code. Change-Id: I61ba602af78d546a91cf009ae7350cf03eaa84dd Reviewed-on: https://chromium-review.googlesource.com/305880 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Tryjob-Request: Corentin Wallez <cwallez@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>