Retire JumpList favicon loading related UMA histograms

This CL retires WinJumplist.OnFaviconDataAvailableDuration and
WinJumplist.StartLoadingFaviconDuration as crbug/717236 is fixed and
verified.

BUG=717236

Review-Url: https://codereview.chromium.org/2956553002
Cr-Commit-Position: refs/heads/master@{#483467}
2 files changed