libweave: base::Value refactor (1/n)

Remove old base::APIs that would be removed after libchrome r890000
uprev, including:
  * DictionaryValue::Get{,Boolean}WithoutPathExpansion
  * DictionaryValue::empty
  * ListValue::begin/end

BUG=chromium:1099111, b:190446478
TEST=FEATURES=test emerge-hatch libweave

Change-Id: I3e9b2980278e8ce42272002fc55a1be3c406764c
Reviewed-on: https://chromium-review.googlesource.com/c/weave/libweave/+/3017629
Tested-by: Grace Cham <hscham@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Commit-Queue: Grace Cham <hscham@chromium.org>
4 files changed