BUG/BUILD: replace haproxy-systemd-wrapper with $(EXTRA) in install-bin.

[wt: this should be backported to 1.6 and 1.5 as well since some platforms
 don't build the systemd-wrapper]
diff --git a/Makefile b/Makefile
index 4f0aa8a..84b1f78 100644
--- a/Makefile
+++ b/Makefile
@@ -805,10 +805,9 @@
 		install -m 644 doc/$$x.txt "$(DESTDIR)$(DOCDIR)" ; \
 	done
 
-install-bin: haproxy haproxy-systemd-wrapper
+install-bin: haproxy $(EXTRA)
 	install -d "$(DESTDIR)$(SBINDIR)"
-	install haproxy "$(DESTDIR)$(SBINDIR)"
-	install haproxy-systemd-wrapper "$(DESTDIR)$(SBINDIR)"
+	install haproxy $(EXTRA) "$(DESTDIR)$(SBINDIR)"
 
 install: install-bin install-man install-doc