postfix: Don't disable IPv6 for gmail.com

I think it was added to improve the mail reputation (avoid being
filtered as spam), but at lot has changed since it was added (+5 years
ago), so let's remove it.

roles/postfix/handlers/main.yml

@@ -9,7 +9,6 @@
 - name: Postmap additional files  # noqa no-changed-when
   command: postmap /etc/postfix/{{ item }}
   loop:
-    - transport
     - domains
     - msa_header_checks
 

roles/postfix/tasks/main.yml

@@ -6,7 +6,6 @@
   loop:
     - main.cf
     - master.cf
-    - transport
     - transport.pcre
     - aliases
   notify:

roles/postfix/templates/main.cf.j2

@@ -162,7 +162,6 @@ local_recipient_maps =
 relay_domains =
 
 transport_maps =
-  ${indexed}/transport
   pcre:${config_directory}/transport.pcre
 
 wiki_bouncehandler_destination_recipient_limit = 1

roles/postfix/templates/master.cf.j2

@@ -68,8 +68,6 @@ flush     unix  n       -       n       1000?   0       flush
 proxymap  unix  -       -       n       -       -       proxymap
 proxywrite unix -       -       n       -       1       proxymap
 smtp      unix  -       -       n       -       -       smtp
-smtp-ipv4      unix  -       -       n       -       -       smtp
- -o inet_protocols=ipv4
 relay     unix  -       -       n       -       -       smtp
 #       -o smtp_helo_timeout=5 -o smtp_connect_timeout=5
 showq     unix  n       -       n       -       -       showq

roles/postfix/templates/transport.j2

-#
-# {{ansible_managed}}
-#
-
-#lists.archlinux.org mailman:
-gmail.com smtp-ipv4: