component updater: replace DCHECK with CHECK where appropriate

Some DCHECKS have been removed.

I ran the code under the debugger and the bulk of the code
(such as UpdaterState::Serialize or
 UpdaterState::NormalizeTimeDelta) is definitely covered by the
unit tests, on Windows. It's possible the the coverage is
undereported because it is a branded build.

Low-Coverage-Reason: COVERAGE_UNDERREPORTED
Fixed: b/41490341
Change-Id: I4d56159babb8957360441580dc6c3340e93510f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5542330
Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Commit-Queue: Sorin Jianu <sorin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1302102}