Bluetooth: fix -Wdefaulted-function-deleted warnings.

Some types had explicitly defaulted constructors even though they
are not actually default-constructible. Also fixes an unused
variable warning.

Tag: #refactor
Bug: 241680050
Test: atest --host bluetoothtbd_test net_test_osi
Change-Id: Ieea664fe7c6ecdca6be352777c775dfd4649e5bd