[quickview] Remove redundant metadata size @keyframes selector

The same selector was repeated twice: one is sufficient. Add TODO's to
fix various issues with this metatdata size loading animation.

Bug: 965370
Change-Id: Ifa80818f2f570fc1ecbb6edcd87c5961cb9a2cd2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1684832
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#673950}