Remove unused preload-related enums

Bug: 652228
Change-Id: Ifa4d7b32b2fe5c05884c2ce2dc128a910433b71b
Reviewed-on: https://chromium-review.googlesource.com/544379
Commit-Queue: Takeshi Yoshino <tyoshino@chromium.org>
Reviewed-by: Takeshi Yoshino <tyoshino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#481553}
2 files changed