Remove sign-in and field trial related codes from GCM.

These codes are not longered needed after GCM is enabled for all users.

BUG=447016
TEST=tests updated
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Review URL: https://codereview.chromium.org/824823003

Cr-Commit-Position: refs/heads/master@{#310667}
16 files changed