Bluetooth: AMP: Remove dead code

Remove code which cannot execute. l2cap_conn_add for AMP_LINK
might only be invoked when receiving data in l2cap_recv_acldata.
But this case is checked in the first statement there.

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>