Bluetooth: gatt: Fix automatic resubscription causing CCC removal

This fixes CCC subscriptions that were removed if the automatic
resubscription was aborted by ACL disconnection.
As the client renews subscriptions, there is no point of removing those
if the link is disconnected unexpectedly.
The API user won't be notified about the failure, as the automatic
resubscriptions are implicit, and after reconnection the subscriptions
will be still valid.

Signed-off-by: Mariusz Skamra <mariusz.skamra@codecoup.pl>