Remove redundant logic dealing with multiple TX domains

[martijnbastiaan]

After merging #688, we can remove all code dealing with multiple TX domains. The easiest way is probably to change:

bittide-hardware/bittide/src/Bittide/Transceiver.hs

Lines 175 to 176 in c92c648

	{ txClocks :: Vec n (Clock tx)
	-- ^ See 'Output.txClock'

to

 { txClock :: Clock tx
 -- ^ See 'Output.txClock' 

and see where the type errors lead.