OSSystemExtensionErrorRequestCanceled is called when the activation
delegate returns OSSystemExtensionReplacementActionCancel on request
actionForReplacingExtension withExtension. As per the previous (parent)
commit we no longer request cancellation, so we can be sure that
receiving a "cancelled" error is an actual error and not something that
is supposed to happen.
This commit also removes the "error" from the log prefix, as the message
sent may also be a warning instead, and the LOG_LEVEL conveys the
severity of the log line anyways.
1781289f22