Revert "Bluetooth: Update sec_level/auth_type for already existing connections"

This reverts commit 04530982. That
commit is wrong for two reasons:

- The conn->sec_level shouldn't be updated without performing
authentication first (as it's supposed to represent the level of
security that the existing connection has)

- A higher auth_type value doesn't mean "more secure" like the commit
seems to assume. E.g. dedicated bonding with MITM protection is 0x03
whereas general bonding without MITM protection is 0x04. hci_conn_auth
already takes care of updating conn->auth_type so hci_connect doesn't
need to do it.

Signed-off-by: Johan Hedberg <johan.hedberg@nokia.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>