floss: Migrate base::Bind for do_in_main_thread

base::Bind was deprecated. Use base::BindOnce for the second argument of
do_in_main_thread since the function expects a base::OnceCallback.

This is a mechanical change by replacing base::Bind with base::BindOnce
for do_in_main_thread.

Bug: 272116782
Tag: #floss
Test: FEATURES=test emerge-volteer floss
Change-Id: Ia5010575c6302cd45c9977816e3e99a96c4d8d0d