Remove duplication.

Makefile

@@ -22,7 +22,6 @@ all: uninstall clean install
 	make -C cmd/metrics-bench uninstall clean install
 
 uninstall:
-	rm -f $(GOROOT)/pkg/$(GOOS)_$(GOARCH)/$(TARG).a
 	rm -f $(GOROOT)/pkg/$(GOOS)_$(GOARCH)/$(TARG).a
 	rm -rf $(GOROOT)/src/pkg/$(TARG)
 	make -C cmd/metrics uninstall