synth_sf2: purge on last clean
synth_sf2: purge on last clean

LiberoSoc don't like unused nets.

YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys