This reverts commit 287a4a0429.
As Marek correctly pointed out, sync functions cannot be run async against one another even if run inside an async function
(the python interpreter will remain active until the next yield and that's at the end of the sync func / inside the async function).
--> So there's no need for a lock.
I still cannot protect against assumptions made by sync code authors about blocking the Qubes OS main loop. Those will be broken.
Moreover the code of this commit was botched anyway.
3db5e9f8bf