IndexedDB: Remove UMA collection for total database open time

These metrics were added here: https://crrev.com/470373002

From a review of whether we use this today, these are no longer
used/needed.

Bug: 717812, 397552, 395799
Change-Id: I1b296832a7ed87fb9653be9eb83cc2b3eb8ef6b1
Reviewed-on: https://chromium-review.googlesource.com/c/1336429
Commit-Queue: Chase Phillips <cmp@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Reviewed-by: Chris Mumford <cmumford@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608613}
4 files changed