Floss: remove workaround that skips MSBC for Flex

This CL removes the workaround for Flex. This should be merged only
after crrev.com/c/5312827 has merged.

Bug: 321180937
Test: m Bluetooth
Flag: EXEMPT floss only changes
Change-Id: I64e2488300c75e0826692b8186f9d905a97dbf5c