Allow framing Dimension

Fix regression since 2a50b8b6bb (#597).

Dimension is intended to be embedded in various clients,
be it the Element service that we host (at element.DOMAIN),
some other Element (element-desktop running locally), etc.

roles/matrix-nginx-proxy/templates/nginx/conf.d/matrix-dimension.conf.j2

@@ -5,7 +5,6 @@
 	gzip_types text/plain application/json application/javascript text/css image/x-icon font/ttf image/gif;
 	add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;
 	add_header X-Content-Type-Options nosniff;
-	add_header X-Frame-Options SAMEORIGIN;
 {% for configuration_block in matrix_nginx_proxy_proxy_dimension_additional_server_configuration_blocks %}
 	{{- configuration_block }}
 {% endfor %}