Retire 'alertmanager' public endpoint, unused

Karma will proxy all calls through itself, thus the 'alertmanager'
public endpoint is not needed anymore.

services.yml.default

@@ -139,10 +139,6 @@ prometheus:
       port: 9090
       scheme: http
       enable_sso_proxy: true
-    - name: alertmanager
-      port: 9093
-      scheme: http
-      enable_sso_proxy: true
     - name: prober
       port: 9115
       scheme: http

services.yml.no-elasticsearch

@@ -105,10 +105,6 @@ prometheus:
       port: 9090
       scheme: http
       enable_sso_proxy: true
-    - name: alertmanager
-      port: 9093
-      scheme: http
-      enable_sso_proxy: true
     - name: prober
       port: 9115
       scheme: http