Remove old DCHECK from ~PepperStreamChannel().
Remove old DCHECK from ~PepperStreamChannel().

Now channel_ can be owned by the ChannelAuthenticator, so the assumption
verified by this DCHECK is not valid anymore.

BUG=105214

Review URL: http://codereview.chromium.org/8989068

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@116105 0039d316-1c4b-4281-b951-d872f2087c98

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