Remove PreviewsReloadsAreSoftOptOuts feature flag

This behavior is enabled by default and something we no longer need a
flag for.

Change-Id: I06b8abd12087c08aa53d970a15c2a61fa837a50c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1622309
Reviewed-by: Doug Arnett <dougarnett@chromium.org>
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661873}
5 files changed