Simplify postfix package handling

It is only one package for all listed distributions.

postfix/init.sls

@@ -1,15 +1,10 @@
 {% from "postfix/map.jinja" import postfix with context %}
 
 postfix:
-  {% if postfix.packages is defined %}
   pkg.installed:
-    - names:
-  {% for name in postfix.packages %}
-        - {{ name }}
-  {% endfor %}
+    - name: {{ postfix.package }}
     - watch_in:
       - service: postfix
-  {% endif %}
   service.running:
     - enable: True
     - require:

postfix/map.jinja

@@ -1,24 +1,24 @@
 {% set postfix = salt['grains.filter_by']({
     'Debian': {
-        'packages': ['postfix'],
+        'package': 'postfix',
         'postgrey_pkg': 'postgrey',
         'service': 'postfix',
         'aliases': '/etc/aliases',
     },
     'Gentoo': {
-        'packages': ['mail-mta/postfix'],
+        'package': 'mail-mta/postfix',
         'postgrey_pkg': 'mail-filter/postgrey',
         'service': 'postfix',
         'aliases': '/etc/mail/aliases',
     },
     'RedHat': {
-        'packages': ['postfix'],
+        'package': 'postfix',
         'postgrey_pkg': 'postgrey',
         'service': 'postfix',
         'aliases': '/etc/aliases',
     },
     'Arch' : {
-        'packages': ['postfix'],
+        'package': 'postfix',
         'postgrey_pkg': 'postgrey',
         'service': 'postfix',
         'aliases': '/etc/aliases',