change(all): deprecate provider_ip config field

- change should not affect any existing configurations
- change solves issues with dual stack updates (#767)
- was unneeded and adds unneeded complexity

docs/servercow.md

@@ -13,7 +13,6 @@
           "username": "servercow_username",
           "password": "servercow_password",
           "ttl": 600,
-          "provider_ip": true,
           "ip_version": "ipv4",
           "ipv6_suffix": ""
       }
@@ -32,7 +31,6 @@
 - `"ttl"` can be set to an integer value for record TTL in seconds (if not set the default is 120)
 - `"ip_version"` can be `ipv4` (A records), or `ipv6` (AAAA records) or `ipv4 or ipv6` (update one of the two, depending on the public ip found). It defaults to `ipv4 or ipv6`.
 - `"ipv6_suffix"` is the IPv6 interface identifier suffix to use. It can be for example `0:0:0:0:72ad:8fbb:a54e:bedd/64`. If left empty, it defaults to no suffix and the raw public IPv6 address obtained is used in the record updating.
-- `"provider_ip"` can be set to `true` to let your DNS provider determine your IPv4 address (and/or IPv6 address) automatically when you send an update request, without sending the new IP address detected by the program in the request.
 
 ## Domain setup