Remove LOG << "Changing alternative service".
Remove LOG << "Changing alternative service".

Remove LOG(WARNING) for changing alternative service in preparation for multiple
alternative services per host.
* This statement was not entirely correct to start with, because it also also
  got logged when no stored alternative service got modified, only the one added
  shadowed the alternative service of the canonical host.
* With multiple alternative services per host, adding one to a host will not
  change an existing one.

BUG=392575

Review URL: https://codereview.chromium.org/1188543002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#335079}

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