has_client.cc: cleanup device when GATT operations may be pending

We should clear device that is getting disconnected after it was already
disconnected, otherwise it's GATT queue may have pending elements that
will belong to next device that gets same connection ID.

Bug: 361721967
Test: atest --host --no-bazel-mode bluetooth_has_test
Change-Id: Iea06ff952e78534cf672fc1296f220e52e89ac84