Remove base::Value::GetType()

This change replaces remaining usages of base::Value::GetType() with
base::Value::type() and removes the deprecated method entirely.

Bug: 646113
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I412454d05f56d94125a76e06a09990e2d6a424e9
Reviewed-on: https://chromium-review.googlesource.com/718458


Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518287}