Delete bt_snoop.log when snoop logging is disabled

This patch will immediatly delete the snoop log if Bluetooth is on. If Bluetooth
is off it will delete the log as soon as Bluetooth starts again.

Test: Turn off logging while Bluetooth is on and off
Bug: 36718948
Change-Id: Ib660cd442c93f1a34c948d51c5cffc38695558d5