Bluetooth: Fix removing connection parameters when unpairing

The commit 89cbb063

 introduced support for deferred connection
parameter removal when unpairing by removing them only once an
existing connection gets disconnected. However, it failed to address
the scenario when we're *not* connected and do an unpair operation.

What makes things worse is that most user space BlueZ versions will
first issue a disconnect request and only then unpair, meaning the
buggy code will be triggered every time. This effectively causes the
kernel to resume scanning and reconnect to a device for which we've
removed all keys and GATT database information.

This patch fixes the issue by adding the missing call to the
hci_conn_params_del() function to a branch which handles the case of
no existing connection.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Cc: stable@vger.kernel.org # 3.19+