roles/dch-proxy: Remove backend myala

*myala.pyrocufflink.jazz* no longer hosts any public-facing websites,
and is in fact shut down. To prevent HAproxy from failing to start
because it cannot resolve the name, this backend needs to be removed.

roles/dch-proxy/templates/backend-myala.haproxy.cfg.j2

@@ -1,7 +0,0 @@
-backend myala
-    server myala myala.pyrocufflink.jazz:80 check
-
-
-backend myala-tls
-    mode tcp
-    server myala myala.pyrocufflink.jazz:443 check