floss: Log pretty UUID in DBus debugging log

It was printed as "array of u8" so was hard to read.

This patch also removes the RefArgToRust impl for Uuid because it's not
used. This is only needed for those underlying types that are used as
DBusType.

Bug: 342337056
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: manual Toggle BT, verify the log
Flag: EXEMPT, Floss-only changes
Change-Id: Iac9352b9bb1eb21455c12033c852f8dda0699963