Remove ZoninatorSniff

[rebeccahum]

Since all sites have moved from .com, we can remove the sniff since REST API is loaded by default.

  * This sniff reminds the developers to check whether the WordPress Core REST API is enabled

• along with loading v0.8 and above.

VIP-Coding-Standards/WordPressVIPMinimum/Sniffs/Compatibility/ZoninatorSniff.php

Line 75 in 60ad148

$message = 'Zoninator of version >= v0.8 requires WordPress core REST API. Please, make sure the `wpcom_vip_load_wp_rest_api()` is being called on all sites loading this file.';

Not to mention that the function mentioned in the error message is deprecated:

https://github.com/Automattic/vip-go-wpcom-compat/blob/79bce981b331c7ed9e608f06b2407f976dac9235/wpcom-deprecated-functions.php#L9

[jrfnl]

Action plan suggestion:

1. Deprecate the sniff in the next release (2.x) by:
   1. Adding a deprecation warning to the sniff which will inform people to remove the sniff reference from their own custom ruleset.
   2. Silencing all messages from the sniff from within the VIPMinimum ruleset, effectively removing the sniff already for people using the standard rulesets.
2. Remove the actual sniff in the next major, i.e. 3.0.0.

Loosely related to #600