Slightly simplify @DIST@ substitution in repository definition

Makefile

@@ -162,7 +162,7 @@ install-sysvinit: install-init
 
 install-rh: install-systemd install-systemd-dropins install-sysvinit
 	install -D -m 0644 misc/qubes-r4.repo.in $(DESTDIR)/etc/yum.repos.d/qubes-r4.repo
-	DIST='$(DIST)'; sed -i "s/@DIST@/$$(echo $${DIST%%[0-9]*})/g" $(DESTDIR)/etc/yum.repos.d/qubes-r4.repo
+	DIST='$(DIST)'; sed -i "s/@DIST@/$${DIST%%[0-9]*}/g" $(DESTDIR)/etc/yum.repos.d/qubes-r4.repo
 	install -d $(DESTDIR)$(LIBDIR)/yum-plugins/
 	install -m 0644 misc/yum-qubes-hooks.py* $(DESTDIR)$(LIBDIR)/yum-plugins/
 	install -D -m 0644 misc/yum-qubes-hooks.conf $(DESTDIR)/etc/yum/pluginconf.d/yum-qubes-hooks.conf