Use a map directly for the noindex header value

Another case of 'if is bad' in NGINX config. Better to just use
a map with a default empty value.

roles/float-infra-nginx/templates/config/conf.d/noindex.conf

 # Global map used to forcefully prevent indexing of specific URLs.
 # Configure via drop-in files in /etc/nginx/noindex/.
 
-map $host$uri $noindex_url {
-    default 0;
+map $host$uri $noindex_header {
+    default '';
 
     include /etc/nginx/noindex/*.conf;
 }

roles/float-infra-nginx/templates/config/noindex/README.md

@@ -21,10 +21,10 @@ this directory. The files should contain one entry per line, with the
 syntax](http://nginx.org/en/docs/http/ngx_http_map_module.html):
 
 ```
-"example.com/path/"  1;
+"example.com/path/"  noindex;
 ```
 
-The value should always be set to 1.
+The value should always be set to `noindex`.
 
 Deindexing via HTTP header is described here:
 

roles/float-infra-nginx/templates/config/snippets/site-common.conf

@@ -76,6 +76,5 @@ location {{ ep.path }}/ {
 {% endfor %}
 {% endfor %}
 
-if ($noindex_url) {
-	add_header X-Robots-Tag noindex;
-}
+add_header X-Robots-Tag $noindex_header;
+