Revert #10388: 'Fix BIDIR UART issue' in maintenance branch.

[mikeller]

Reverting because of problems described in #10435 - we need more time to investigate / fix.

[tonycake]

Sorry guys, reverting a change that fixes potentially serious issues with control (any single-wire Rx), for something that fixes vTx control is nuts.
Mike, you mentioned that we might need a flag to let Smart audio live with the previous (bad) behaviour. That might be how we need to handle this. If you need me to code this up, I am happy to.
I am not happy to see this critical fix un-done though.

[mikeller]

@tonycake: This is only reverting this for the current maintenance branch - this does not affect the master branch that will eventually become 4.3.
It is Betaflight policy to manage maintenance / patch release in such a way that they only contain uncontroversial bugfixes and changes that are safety relevant, in such a way that users with a currently working setup on a given release can update to the next patch version of the same release without having to worry about their setup breaking.
In this light, cherry-picking #10388 into the maintenance branch was the wrong decision, as it turned out to break currently working setups - apologies for that.