Bluetooth: Remove redundant check for ACL_LINK

The encryption key size is read only for BR/EDR (ACL_LINK) connections
so there's no need to check for it in the read_enc_key_size_complete()
callback.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>