Fix chromeos::kMaxValue symbol duplication

It is part of both FeatureFlagsMigrationStatus and PrinterSetupResult
enums. This CL makes the first of them a class enum.

Bug: 1101837
Change-Id: Idc1540cd2f1e1b82e4a06b4822f3c6b365514897
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2659344


Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Henrique Ferreiro <hferreiro@igalia.com>
Cr-Commit-Position: refs/heads/master@{#848816}