techmap: don't drop attributes on replaced cells.
techmap: don't drop attributes on replaced cells.

This was introduced in 76c4ee4ea5cb6a3dc214f66237af22a1bedda010.

Fixes #2204.

YosysHQ/yosys,SymbiFlow/yosys,SymbiFlow/yosys,cliffordwolf/yosys,SymbiFlow/yosys,YosysHQ/yosys,YosysHQ/yosys,antmicro/yosys,YosysHQ/yosys,cliffordwolf/yosys,antmicro/yosys,cliffordwolf/yosys,cliffordwolf/yosys,cliffordwolf/yosys,SymbiFlow/yosys,cliffordwolf/yosys,YosysHQ/yosys,cliffordwolf/yosys,antmicro/yosys,antmicro/yosys,SymbiFlow/yosys,antmicro/yosys,cliffordwolf/yosys,antmicro/yosys,SymbiFlow/yosys,antmicro/yosys,cliffordwolf/yosys,YosysHQ/yosys,SymbiFlow/yosys,YosysHQ/yosys,SymbiFlow/yosys,YosysHQ/yosys,antmicro/yosys