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The session commit delay is always overridden in production. As such, the
default only affects test, where it makes it much more likely to time out.
Remove it and re-enable the disabled sessions integration tests.

BUG=263369, 232313

Review-Url: https://codereview.chromium.org/2389443003
Cr-Commit-Position: refs/heads/master@{#422668}