Cleanup JingleInfoRequest on JingleSessionManager::Close
Cleanup JingleInfoRequest on JingleSessionManager::Close

If NAT traversal is turned on then JingleInfoRequest adds itself as a
listener to the signal strategy.  Delete the request in
SessionManager::Close so that it removes itself as a listener and
signal strategy can be cleaned up.

BUG=108212
TEST=none


Review URL: http://codereview.chromium.org/9004024

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@115210 0039d316-1c4b-4281-b951-d872f2087c98

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