libweave: remove base::ValueReferenceAdapter

Was used for libchrome uprev migration.

BUG=chromium:909719
TEST=unit tests

Change-Id: I206f314d6352a3e3c7f4abdb1c5cf8206ea7e32a
Reviewed-on: https://chromium-review.googlesource.com/c/weave/libweave/+/2050287
Tested-by: Grace Cham <hscham@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Commit-Queue: Grace Cham <hscham@chromium.org>
3 files changed