Get rid of warning when connecting LE device

We are sending LE fixed channel notification to classic callback. Stop
doing that. This triggers following warning in log output on every
LE connection:
W bt_smp  : smp_br_connect_callback is called on unexpected transport 2

Test: manual with phone, verify warning is gone when connecting over LE
Change-Id: I47597fa03744fb1bff03d287f790ea32fa033cc7