opt_clean - remove unused cells and wires

yosys> help opt_clean
opt_clean [options] [selection]
This pass identifies wires and cells that are unused and removes them. Other
passes often remove cells but leave the wires in the design or reconnect the
wires but leave the old cells in the design. This pass can be used to clean up
after the passes that do the actual work.

This pass only operates on completely selected modules without processes.
also remove internal nets if they have a public name