Floss: Add logs to debug lost bond

Repro is difficult, so this adds logs so that this issue can be debugged
when there is a feedback report. Covers two hypotheses:
* remove_bond is called by client, or
* device is dropped when migrating config from BlueZ

Bug: 255849761
Tag: #floss
Test: Build on Chrome OS and Linux

Change-Id: I2c8adecb78fdfcf4c953b75a87a3b7908b0e0555