Removing safe_browsing::features to not clash with ::features

According to the coding style guide a sub-namespace should not
have the same name as a common top level namespace. That still
happens with many "features" namespaces which causes problems
whenever the compiler knows about the root ::features namespace.

This patch removes the namespace completely and lets the
constants live in the safe_browsing namespace directly, making
the code a little shorter.

Another option would have been to rename the namespace from
::safe_browsing::features to ::safe_browsing_features like was
recently done to some other features namespaces, for instance app_list_features.

Change-Id: I3655cca7fb56b45a03118a80a957599bd5f316b3
Reviewed-on: https://chromium-review.googlesource.com/c/1251604
Commit-Queue: Daniel Bratell <bratell@opera.com>
Reviewed-by: Varun Khaneja <vakh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596179}
4 files changed